Choosing Sub Panel

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Old 12-13-18, 04:40 PM
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Choosing Sub Panel

I'm planning to put in a new sub-panel to feed my new 24'x24' addition. My existing home has a square D QO panel so plan to buy the same for consistency. Circuit plans are as follows:

Circuit 1 for entertainment room receptacles. (Total of 9 duplex)

Circuit 2 for two bedrooms receptacles and 3 outside receptacles. (Total of 15 duplex)

Circuit 3 is for Bathroom GFCI by sink. (Total of 2 duplex)

Circuit 4 is for Pump/motor of Jetted tub.

Circuit 5 is for lighting throughout addition and smoke alarms. (16 12w recessed LED, Vanity light with 3 bulbs, 2 fan/light combos, 1 closet light, 1 bath fan/light, 1 patio light, 1 crawl space entrance light in basement, 1 attic entrance light. 4 hardwired smoke alarms.

Circuit 6 is for in line heater for jetted tub if we decide to go that route (Havn't purchased heater yet but we are considering it at this time).


Does this one for amazon look good for what I'm planning to do? Recommendations? I was originally looking for a 12 space panel but was having trouble finding one.

https://www.amazon.com/Square-Schnei...ct_top?ie=UTF8
 
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Old 12-13-18, 05:23 PM
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Great choice. And this is to meet the 25 characters needed????
 
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Old 12-13-18, 07:20 PM
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What wire do I need to buy to feed this sub panel? With the mentioned circuits planned and all being on a 20 amp breaker, what size main panel breaker should I get? Please account for possibly adding some circuits in the future.
 
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Old 12-13-18, 07:41 PM
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I normally choose 60 amps for ease of available materials. (wire, circuit breaker) 60 amps will also do everything you want and then some.

You will need #6 copper wire or cable.
 
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Old 12-13-18, 08:07 PM
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I normally choose 60 amps for ease of available materials. (wire, circuit breaker) 60 amps will also do everything you want and then some.

You will need #6 copper wire or cable.

It's possible that a heat pump may also be fed from this panel as well. Awaiting HVAC options from a guy right now. I can extend my current ductwork and not do the heat pump but would have to upgrade my propane furnace also. So which route I go depends on the cost for each I guess. I'm not a HVAC whiz by any means.


With this said, do you think 60A is still the best route or just go with a 100A to be more then safe?
 
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Old 12-14-18, 09:03 AM
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You need to do an anticipated max load calculation to properly size the feeder. This is calculated using the actual amp draw of attached devices/equipment, not just by adding up the breaker sizes for different circuits.
 
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Old 12-14-18, 10:26 AM
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Some of these circuits.will require either afci or afci/gfi protection. Depends on what code cycle is enforce.
 
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Old 12-14-18, 11:40 AM
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Great choice. And this is to meet the 25 characters needed????


.............................................
 
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Old 12-14-18, 08:09 PM
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Some of these circuits.will require either afci or afci/gfi protection. Depends on what code cycle is enforce.
I've purchased 4 cafci/gfci breakers and 3 cafci breakers. I'm covered in that regard.


You need to do an anticipated max load calculation to properly size the feeder.
Seeing as you said max load calculation, I'm assuming that means if all lights are on and something is plugged into all receptacles as well as furnace running or central AC in the summer time, range on full blast, refrigerator, microwave, etc .? Suggestions on where to start for figuring max load calcs? I want to do this in the AM so I can get wire for the sub panel.

Thanks
 
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Old 12-15-18, 08:05 AM
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Google "load calculation" and you will find some sites that should help.

Really, all you need to do is to add up the known loads that will be on the sub panel. (Microwave, heating/cooling, spa tub, lighting, etc) and you can use 180VA (watts) for the unknown loads per receptacle.
 
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Old 12-15-18, 08:11 AM
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Google "load calculation" and you will find some sites that should help.

Really, all you need to do is to add up the known loads that will be on the sub panel. (Microwave, heating/cooling, spa tub, lighting, etc) and you can use 180VA (watts) for the unknown loads per receptacle.
I知 going to do a load calc today and I値l post the results after.
 
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Old 12-15-18, 09:30 AM
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When I said anticipated max load, I mean you need to consider what the maximum load will be of the items that may or most likely be on at the same time. So yeah... the HVAC, water heater, oven, some lighting, TV, you just don't need to get into the realm of everything you have is on at once.
 
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Old 12-15-18, 09:22 PM
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When I said anticipated max load, I mean you need to consider what the maximum load will be of the items that may or most likely be on at the same time. So yeah... the HVAC, water heater, oven, some lighting, TV, you just don't need to get into the realm of everything you have is on at once.
thanks . I'll try and anticipate my load as you've suggested and see where I'm at. I dont believe adding a 100A panel box with a 100A disconnect would be an issue with overloading but it's definantly best to check it out first.
 
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Old 12-17-18, 10:38 PM
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Received my 100A Square D QO panel box today and breakers will be here within next 2 days. I only have a few home runs to make. Rest of the circuits are wired up and ready to be inspected. I'm debating on whether to install a 60 or 100A disconnect. Still have to work on the load calc and go from there. I have a roughly a 1400 SF house prior to addition being built so I dont think there will be an issue with overloading. Is there any other parts I need other then the jumper wire between my two panel boxes to purchase to complete my sub panel box installation? I'm a complete newbie with this part of the work. I'll post a pic of the panel box just in case it helps.

Thanks for everyones help thus far. Have helped me through many aspects of my project through multiple threads!


https://imgur.com/a/MkZrqFe
 
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Old 12-18-18, 11:13 AM
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Its hard to beat a 60 amp subpanel. #6 copper wire is sufficient as long as it isn稚 too long of a run. There are charts you can find in regards to proper wire sizing. # 6 wire is rated for 55 amps but National Electric Code lets you step up to 60 anps because 55 amp breakers are not common. I知 assuming the addition is attached to the rest of the house. If thats the case nake sure that the subpanel isnt neutral bonded. This is a common mistake made by many oeople. There is usually a jumper that can be removed to isolate the ground and neutral bars in the sub panel. Also take into account when calculating your loads that a lot of devices draw a lot more amps when starting (pool pump/tub motor, air compressor motor, etc).
 
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Old 12-18-18, 03:23 PM
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In your opinion, do you think a 60A breaker feed to my sub panel will be enough for what I listed in post #1 as being on this circuit? Circuit 5 will also include 2 outside lights (Not on original post).

I want to leave some room for possibly adding a couple circuits in the future as well. The wife wants a swimming pool and probably some other stuff will be added at some point.
 
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Old 12-18-18, 05:07 PM
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You really gotta take into account how much power you will be using at any given time. Lighting basically uses nothing. Especially iF they are LED. your largest draw sounds like its going to be the tub heater. What is the service amperage coming into your main panel?
 
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Old 12-18-18, 05:29 PM
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you want to size the panel for whatever your continuous load will be. As a rule of thumb you should aim for 80% capacity of the breaker rating which would be 48 amps available for continuous use 24 hrs a day 7 days a week if you do a 60 amp setup. Remember... You WILL NOT being using everything all the same time.
 
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Old 12-18-18, 06:50 PM
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What is the service amperage coming into your main panel?
200 amp disconnect on main panel
 

Last edited by Jrk5230; 12-18-18 at 07:20 PM.
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Old 12-18-18, 07:25 PM
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Yeah so you have plenty of juice coming into your house to do whatever you please. In my opinion a 60 amp would be plenty but if your more comfortble going bigger it wont hurt to oversize it. Just remember that you need to size the wire accordingly. The bigger sub you are trying to go the bigger the wire you need. Big wire gets very hard to work with. So a lot of factors come into play. Length of the run, concealing the wire and getting it from point A to point B or running individual wires in appropriate sized conduit. Possibilities are endless really. It all just depends what you want.
 
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Old 12-20-18, 10:32 PM
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It looks like the jetted tub specs show a combined 21 amps for the motor & heater to be running.. So factor this into account with everything mentioned below that is going to be on this sub panel. Quite possibly could be pushing the 60 amp subpanel limits. We are weighing options for heating and cooling as well for the addition area. The bosch inverted duct system is one option that was presented to us. Looks like the heat pump calls for a minimum circuit ampacity of 24.2. That throws me at 45.2 amps with just the jetted tub and bosch IDS system and no receptacles or LED lights (use tiny bit of power so basically irrelevant). Then I have two ceiling fans and a bathroom exhaust fan. A desktop computer and entertainment center with TV will all be on these circuits.

Does this sound like I need to install a 100A disconnect instead of a 60A?

If we decide against the Bosch IDS system, and upgrade my existing furnace (on main breaker), do you think the 60A will still be sufficient with everything else? Just want to get a feel for what the communities thoughts are on my situation so I can make a final decision and get my inspection done possibly Monday. Thanks
 
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Old 12-21-18, 09:33 AM
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With what you just described I would go with the bigger feeder. I believe 3 gauge wire is sufficient for 100 amps.
 
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Old 12-21-18, 09:58 AM
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A very basic load calculation would be to figure 3 watts per square foot for general purpose lighting and electrical devices, plus the known large loads.

Given that you'll be powering an unknown amount of HVAC, a whirlpool and possibly a pool from this panel I would go with a 90A feeder to a 100A panel (absent a formal load calc). The 90A feeder can be installed with #2-2-2-6 or #2-2-4-6 aluminum SER cable, whichever your local supplier has in stock.

If the HVAC is resolved in some other way, a 60A panel would be fine which you can power from a 60A breaker in the main panel using #6-3/g NM-B Romex cable.
 
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Old 12-21-18, 12:42 PM
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Great info!! Figuring 3 watts per square foot (17.9 amp) and adding that with jet tub motor and heater plus bosch IDS heat pump system, I'm sitting at 63.1 AMPs. 80% of 90 amp = 72 AMP. Believe I would be sitting pretty good with a 90 amp disconnect but would be pushing the 80% of 90 amp breaker if a pool is installed down the road. Debating whether to go 90 or 100 Amp now.

even if its decided not to install the heat pump, my rough load calc is sitting at 39 Amps, just a bit under the 80% mark and would be pushed close by adding pool in future. So either way I slice it, it looks like the 60 Amp disconnect would be close to maxed out or 90 amp if the heat pump is installed. Maybe going with 100 amp is the best option?
 
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Old 12-21-18, 07:05 PM
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Comments to my last post? I have my electrical inspection on monday.
 
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Old 12-21-18, 07:30 PM
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100 amp breaker will be easier to find in stores. I would go 100 amp.
 
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Old 12-21-18, 09:18 PM
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100 amp breaker will be easier to find in stores. I would go 100 amp.

I'm going to install the wire as if the disconnect was a 100 AMP breaker. Does the wire between main panel and sub panel need to be installed prior to having my rough in inspection?


If not, then I can install the wiring like it was a 100A breaker but hold off on purchasing the breaker until the kinks are worked out on my HVAC system.

What size wire do I need to feed sub panel if installing based on if I was using a 100A breaker? Where do I check for conductor temp ratings?
 
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Old 12-22-18, 06:36 AM
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Does the wire between main panel and sub panel need to be installed prior to having my rough in inspection?
If it will be concealed behind the wall/ceiling finish, yes, it will need to be installed for the rough in. (side note: If that walls/ceiling are already finished and the cable will be fished, then no.)

What size wire do I need to feed sub panel if installing based on if I was using a 100A breaker?
If you are using conduit, you will need #4 copper or #2 aluminum. If you are using cable you will need #2 copper or #1/0 aluminum.

Where do I check for conductor temp ratings?
Insulation ratings will be listed on the conductor/cable jacket. However, many non-metallic cables are limited to the 60 degree C rating. THHN and XHHW (the two most used conductors in conduit) are rated 90 degrees.
 
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Old 12-22-18, 08:29 AM
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So if I use the bare wires running in conduit, it can be 4 guage and if I use the insulated/jacketed wire, it has to be 2 guage? Am I understanding that correctly? What do you recommend for safety, conduit or the wire that comes with insulation cover?

Also, the wire between sub panels will be hung from bottom of ceiling joists in basement. Dont think its a good idea to drill holes the entire width of my house in all basement ceiling joists. To be compliant with NEC code, I have to install my wire to a runner board if attaching to bottom of ceiling joists, correct?
 
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Old 12-22-18, 08:43 AM
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Running boards are not needed for larger cables.
 
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Old 12-22-18, 08:58 AM
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Am I understanding that correctly? What do you recommend for safety, conduit or the wire that comes with insulation cover
Yes. I would use which ever is easiest to install. You could also do a mixture of the two, but then you will need a fairly large box and make a splice.

Drilling holes in joists is fine I I would not hesitate to do it, as long as you follow the rules of drilling joists. I am not a fan of running cables on the bottom of joists no matter what size they are.
 
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Old 12-22-18, 09:10 AM
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I would say the wire with the insulation cover already over it is my quickest, easiest route to go. You have me debating on drilling holes lol. Going to see if I have a nice clear and direct path to sub panel and may drill if that's the case. Would feel much safer boring holes and having the wire run above bottom edge of floor joist.
 
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Old 12-22-18, 10:29 AM
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I would say the wire with the insulation cover already over it is my quickest
Just to be clear, all wires has insulation. we are talking about a cable which is a group of wires within an overall jacket. A cable would be the easiest way to go.

However, you may have some difficulty finding a 4-4-4-G copper cable at the home stores and will have to go with aluminum. Or go to an electrical supply store
 
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Old 12-22-18, 11:48 AM
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I was thinking cable, yes.. thanks
 
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Old 12-22-18, 06:48 PM
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Correct me if I知 wrong but I believe the minimum size wire for a 100 amp feeder is 3 AWG copper. You wont be able to find it in big box store unfortunately. Just run jacketed wire and staple it to the bottom of the joists. Thats the easiest route if you have an unfinished basement. Check your local codes though. Some areas require a raceway aroung the cable to protect it.
 
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Old 12-23-18, 07:03 AM
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Feeders in a single family dwelling are allowed to be sized according to 310.15(b)(7). While not carrying the entire load of the dwelling, it will carry the entire load of the addition.
 
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Old 12-23-18, 07:33 AM
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Feeders in a single family dwelling are allowed to be sized according to 310.15(b)(7). While not carrying the entire load of the dwelling, it will carry the entire load of the addition.
After taking a look. 310.15(b)(7) was revoked in 2014 and replaced with a 83% formula. From what I gather you calculate feeder size based off of 83% of the feeder breaker size. So for 100amp breaker, 83% would be 83 amps. So a feeder sized accordingly to feed 83 amps would be acceptable? It basically works out to be pretty much the same as the chart. Also, I believe that the temp rating is determined by the item that has the lowest rating. I知 not an electrician, so I知 welcome to critisism. Love learning new things everyday.
 
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Old 12-23-18, 08:04 AM
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You need to use the tables for the feeder since it's not a feeder providing the total service to the entire dwelling. For 100A you use 75deg which is #3Cu or #1Al.
 
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Old 12-23-18, 11:30 AM
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I forgot that you are using a cable (NM or SE) so you are limited to 60 degree as I mentioned earlier. (post #28)

You need #2 copper or 1/0 aluminum.

@ Pattenp: So you install a 100 amp service in a house and feed it with #4 copper as allowed in 310.15(b)(7) and then install a 100 amp sub panel. You have the feed the sub panel with #3 copper? What sense does that make?
 
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Old 12-25-18, 08:16 PM
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Thanks Iron!

I've been debating what to choose for heating source and was curious of your opinions on this matter. I know this is a electrical forum but still wanted to see what you guys thought.

Here are the options I was given:

Gas Furnace. Provide and install a American Standard 95% efficiency 80,000 BTU propane furnace. Provide and install PVC venting to exterior building. Connect to existing duct. Provide and install 3 new heat runs to addition. Provide and install 2 zones, will provide dampers, controls and wiring to make system complete. Provide digital thermostat in new addition. Provide all electrical connections. Total $6,270.00

Heat Pump Option. Provide and Install Bosch IDS heat heat pump. Would provide 2 ton air handler to heat and cool addition and 1 existing bedroom. Would be located in basement near access to addition craw space. Would provide heat run to existing bedroom. Provide digital thermostat in new addition. Provide all electrical connections.
$7,850.00

Duel Fuel Option. Provide a 3 ton coil on a new 80,000 BTU gas furnace. Heat pump would provide primary heating down to a set outdoor temperature, then propane furnace would supplement heat pump. Provide and install a American Standard 95% efficiency 80,000 BTU propane furnace. Provide and install PVC venting to exterior building. Connect to existing duct. Provide and install 3 new heat runs to addition. Provide and install 2 zones, will provide dampers, controls and wiring to make system complete. Provide digital thermostat in new addition. Provide all electrical connections. $10,200.00


Had a 2nd guy up and he likes to install the ductless system but said it will cost ~10k.

I'm leaning towards an upgrade of my existing 60000 BTU propane furnace and just adding 3 runs from my existing duct trunk to feed over to addition. This way I would only be paying for propane and not propane for existing house and higher electric bill for added heat pump. Seems this would be my most cost effective method. But also, not sure how this would throw off the balancing of my existing ducts.. I'm struggling mightly with the HVAC part and dont have a ton of knowledge on the subject matter.
Note* I have a 3 ton central AC unit as well that is big enough to handle the extra load the 24'x24' addition adds to the system. Therefore another reason a heat pump doesn't seem like the best option.
 
 

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