Split Bus Panel Question

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Old 03-10-17, 01:27 PM
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Split Bus Panel Question

Just a quick sanity check: I have a split bus main panel in my '76 split-level and the 'Main' to the second bus (all the outlets and lights in my home) is fed by a 60A breaker and a 2 AWG copper jumper. Is there any issue with me upgrading that 60A breaker to 100A? I'm planning to run 75A out to a garage and will obviously need to have more capacity.
 
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Old 03-10-17, 01:37 PM
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Normally the heavy loads are kept in the top of the panel.

It sounds like a panel replacement is in your future.
Can you post a picture of the panel for us ? http://www.doityourself.com/forum/el...-pictures.html
 
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Old 03-10-17, 01:58 PM
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That 20A 2 pole breaker in the middle on the right is the spot where I had planned to put the line to the garage (it goes to my table saw that'll be moving out there as well). I really don't want to pay 2k+ to get a new panel, is there any specific code violation in my current plan?

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Old 03-10-17, 04:44 PM
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What does the panel label show as options? The bottom half was most likely never tested at 100 amp. Violating a UL listing would be the code violation.

What about installing a sub panel next to this main? Move the dryer and water heater over to it.
 
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Old 03-10-17, 05:00 PM
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You've got a lot of heavy 240v circuits there. It looks like you're really pushing a 100A service.
 
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Old 03-10-17, 05:07 PM
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I always thought those split bus panels were 125 amps or higher.
 
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Old 03-10-17, 05:15 PM
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The top has the furnace, dryer, range, water heater, heat pump, then the house main. I don't recall the panel having a amp rating on it but I'll double check when I get home. Work was done to install my heat pump a couple years ago and it was inspected so I would have hoped they would have mentioned if something was amiss.
 
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Old 03-10-17, 05:16 PM
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The panel could be rated to 125A but it's not likely to have a 125A service feeding it.

Electric furnace ?
 
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Old 03-10-17, 05:32 PM
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Split-bus are always interesting to deal with. For true service rating you need to find out size of service conductors and size of meter base.

Looking at 1978 Couse-Hinds catalog as this picture looks similar to these: LC612ES/F was rated at 150amp, LC612PC was 200amp.
 
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Old 03-10-17, 05:49 PM
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By planning to run the heavy (75 amp) feed to the garage you need to do a "load analysis." How to do that is described at the back of the NEC code book.

The results give the number of watts or number of amperes you need to meet code. This does not rule out having a yet larger service if you know that you will be using certain combinations of appliances, air conditioning, and/or tools at the same time.

It is possible that the results of the load analysis will mean you need to put in a new main panel (and possibly a new service) with a higher amperage rating.
 
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Old 03-10-17, 06:55 PM
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That appears to be a Bryant panel. Bryant split-bus panels were fairly popular in the greater Seattle area in the 1970s. I personally installed two of them and they were both rated at 200 amperes with the 60 ampere sub-main breaker.

Assuming that you have the proper SERVICE, i.e. meter base and all conductors from the service drop to the main lugs, you could install a smaller sub-panel and transfer the water heater wiring to the sub using the freed-up circuit breaker space to feed the sub. I don't think there would be a problem using a 100 ampere CB to feed the sub-panel.

What are the size of the incoming conductors to the panel's main lugs?
 
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Old 03-10-17, 07:48 PM
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It's a Murray, I think? There's the diagram, I would think that means the sub can handle 100A? The service lines are 2/0 AL. Also, I'll be doing 65A for the garage now, don't want to try and mess with 90C stuff. If that's not possible I can go lower on the garage too, naturally I'm trying to wire for as much capacity I can get without having to rewire everything.

Edit: So 2/0 THW AL is only rated to 135A at 75C so obviously that's all I'm working with here.

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Last edited by Temp08; 03-10-17 at 09:58 PM.
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Old 03-10-17, 10:01 PM
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2/0 AL for service conductors were good for 150 amps.

It does look like it is legal to swap the 60 main for a 100. Still would not recommend putting a breaker feeding a sub in the lower half.
 
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Old 03-10-17, 10:28 PM
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150 amp, so not too bad, thanks

May I ask why I shouldn't put the sub breaker on the split? Is it just bad practice, a code violation, or dangerous? Hopefully not all three.
 
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Old 03-11-17, 12:23 AM
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I'm sorry, I meant Murray. I don't know why I wrote Bryant. Maybe because Bryant CBs are listed for use in Murray panels.

Notice that the last four spaces on each side of the lower bus may use tandem breakers. If it were mine I would have no problem in replacing the 60 ampere sub-main breaker with a 100 ampere model, other than the price which might be fairly steep. At that point you could re-connect the clothes dryer to the lower bus (move the existing CB) and that would leave a double space for the new CB to feed the garage/shop. Use tandem CBs as needed to serve all existing circuits as well as room for a few more.

You DO need to do a load calculation figuring the most items you may ever have running at one time to see if the 125-150 ampere service is sufficient. Depending on the outcome of this load analysis you may be just fine. I know for myself, living alone, I NEVER see 150 amperes on my 200 ampere service.
We do know the stab limit for the upper half is clearly marked 100 amps for the position where I'm suggesting connecting a subpanel next to the existing panel.
No, we don't. The label states the lower bus protection is 100 amperes maximum, most likely because of the pigtails to the sub-main circuit breaker. We also know the lower bus bars are rated at 125 amperes.
 
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Old 03-11-17, 06:54 AM
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I have deleted my last two answers. Please follow Furd and the others instructions.
 
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Old 03-11-17, 10:47 AM
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May I ask why I shouldn't put the sub breaker on the split? Is it just bad practice, a code violation, or dangerous? Hopefully not all three.
Bad practice first. It could be a code violation per load calculation. Dangerous because if you do trip the main while working in the garage the lights will go out in the house and your spouse will smack you.

If your sub panel feed is 60amps or higher and you put it on the lower bus then you are simply more likely to trip the main breaker. Also, you running close to the maximum load through bus stabs is more likely to cause a failure, especially in a 40 year old panel.

FYI - The bottom bus was called the lighting and appliance section.
 
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Old 03-11-17, 12:23 PM
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So I think I'll swap out the 60A main for 100A and move the dryer, or water heater, to the lower split. Honestly I'm not going to be running that much in the garage, I just wanted the capacity should my needs change in the future, for now a table saw, compressor, fridge, and maybe space heater in the winter. Getting LED lights too. I may even step down to #8 for $$ and ease of pulling through the existing conduit, previous owner ran Romex through it so obviously it needs to come out.


We also know the lower bus bars are rated at 125 amperes.
For my own education may I ask how we know this?
 
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Old 03-11-17, 02:18 PM
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Look at the picture of the label in post 12. It is right there at the bottom of the label.
 
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Old 03-11-17, 03:26 PM
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Look at the picture of the label in post 12. It is right there at the bottom of the label.
Doh, so it is...

Well I just hooked a vacuum to the conduit in the garage, went to the main panel and felt/heard nothing at the conduit entrance. Should I try to pull some #8 with the existing Romex, or am I now going to be excavating an old conduit?
 
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Old 03-11-17, 05:14 PM
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If it is EMT it is DOA. If PVC what size conduit?
Should I try to pull some #8 with the existing Romex
There should not be "Romex", NM-b, in buried conduit. Nm-b is not rated for wet locations and buried conduit is classified as a wet location. For ease of pulling you need to go back with individual conductors such as THWN.
 
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Old 03-11-17, 06:19 PM
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It appears to be 3/4" PVC, sch 40 I think, can't really read anything on it. Yeah I know Romex can't be used in wet locations, part of why I'd like to replace as well. So right now I have 2 Romex wires going into that conduit from the main panel in my house, it must 'Y' somewhere in the yard, one goes to the garage and the other goes to a shed. To be code compliant I'll need to pull all the NM-B out, I was going to abandon the shed portion since I've never needed power there. I'll run 3 #8 THWN to the garage, black-red-white, and one #10 ground, on a 55A breaker from my main. Keeping neutral and ground bars separated at the garage panel, and installing 2 ground rods, though I've read I may only need one?

Also I think this stuff was done about 2001 when the garage was built, just FYI.

That's the plan so far, really hoping I can avoid digging a trench.
 
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Old 03-11-17, 06:41 PM
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I'll run 3 #8 THWN to the garage, black-red-white, and one #10 ground, on a 55A breaker from my main
#8 is generally used for no more than 40 amps. For 55 amps you need #6 (plus #10 for ground).
black-red-white
Sometimes it is cheaper to use two blacks if you can get a roll cheaper that is long enough to be cut in half for the two blacks.
 
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Old 03-11-17, 06:59 PM
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Ampacity Charts

This is what I've been using, #8 THWN in the 75C copper column. So 55A for over current via next size, or do you not do that on buried feed circuits?

Good point about buying in bulk, thanks
 
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Old 03-11-17, 08:17 PM
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Usually 40 amps is max for #8 but with 75 connectors in both panels THWN can be used at 50 amp.

Just to clarify my "bulk comment" only applies to hots. Neutrals smaller then #4 must be factory white (or gray).
 
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Old 03-11-17, 10:13 PM
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So about that PVC, should I use the Romex to pull my new wires? Why can't I feel the vacuum, is the pipe broken at some point?
 
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Old 03-11-17, 10:45 PM
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So about that PVC, should I use the Romex to pull my new wires?
I'd use it to pull masons twine through if you can get it out.
it must 'Y' somewhere in the yard,
And that may give you a problem getting it out. Maybe they made a splice. You could try filling the conduit with soapy water and letting it set for a while. It may loosen the cable or you may end up with a wet spot in the yard if the conduit is broken somewhere.
 
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Old 03-12-17, 08:37 AM
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That old panel and breakers will not have 75 degree terminals. They may not even be 60 degree rated. You will need to check.
 
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Old 03-12-17, 12:27 PM
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So no where on the panel does it list a temperature rating, nor can I find any information on electrical panel temperature ratings generally? Is this really a thing?

I see various breakers in there rated dual 60/75C.
 

Last edited by Temp08; 03-12-17 at 12:46 PM.
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Old 03-12-17, 12:46 PM
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I think you'll eventually be sorry if you don't upgrade the entire service to 200 amps now with a modern breaker panel.
 
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Old 03-12-17, 12:52 PM
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I think you'll eventually be sorry if you don't upgrade the entire service to 200 amps now with a modern breaker panel.
Why? The capacity is already there...
 
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Old 03-13-17, 10:56 AM
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So I tried pulling on that Romex to see if I could get it to move at all, I'm talking wrapping around a 2x4 and using it as a lever... Didn't budge a mil...

So it looks like I'm digging this thing up, yay!
 
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Old 03-13-17, 03:31 PM
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That old "Romex" may be UF-B (gray) and the PVC just a stub to protect it until it is underground.

Otherwise is there an LB or other pull point on the outside where you can access?
 
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Old 03-13-17, 04:26 PM
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I was just sitting here pondering that very possibility. It IS gray, so I'll have to see. Regardless if I want 240V AND 120V out there I'll need to run new conduit and wire.
 
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Old 03-14-17, 08:54 AM
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What does "split bus" refer to?
I have a "split bus" Murray panel very similar but I have 2 separate groups of breakers in the bottom, each run from it's own Main. I thought THAT was the "split"...?
 
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Old 03-14-17, 10:23 AM
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I think you'll eventually be sorry if you don't upgrade the entire service to 200 amps now with a modern breaker panel.

Why? The capacity is already there...

I cannot even begin to count all the older aluminum bus panels I have seen that burned up because the tension on the old breaker-to-bus connections isn't what it used to be. Face it, you have what was an economy panel back when it was installed and the economy panels aren't exactly known for longevity.
 
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Old 03-14-17, 12:40 PM
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the tension on the old breaker-to-bus connections isn't what it used to be
Sounds like a problem with old breakers.
 
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Old 03-14-17, 03:47 PM
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What does "split bus" refer to?
I have a "split bus" Murray panel very similar but I have 2 separate groups of breakers in the bottom, each run from it's own Main. I thought THAT was the "split"...?
I don't know if they had a name but yours could be described as a dual split bus panel. I see it referred to as a "Dual Main Device. two separate main breakers: two separate branch breaker sections; one set of line lugs"

Split bus means that there are multiple sections to the bus in the panel. So one is fed from the other.
 
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Old 03-15-17, 08:14 AM
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Originally Posted by Astuff
Split bus means that there are multiple sections to the bus in the panel. So one is fed from the other.
Thanks for clarifying that for me.

I'm not a fan of the type but I'm surprised to find out it's an "economy" panel.
 
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Old 03-15-17, 09:30 AM
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I'm not a fan of the type but I'm surprised to find out it's an "economy" panel
They were used as a cheaper alternative to a panel with a main disconnect, why pay for an additional breaker if it's not required? This was disallowed in 1984. Apparently one of the issues was the lower split was sometimes only rated 60A, so if you had a water heater or drier you'd get a lot of nuisance trips of that breaker.

There doesn't appear to be anything inherently "wrong" with these panels, people just seem to equate "cheaper" with "low-quality". Mine is rated 200 amp for the main and 125 amp for the lower split.
 

Last edited by Temp08; 03-15-17 at 09:53 AM.
 

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