Transfer Switch vs Transfer Panel

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  #1  
Old 03-11-06, 10:22 AM
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Join Date: Jan 2005
Location: Sterling Heights
Posts: 308
Transfer Switch vs Transfer Panel

Doing some more research on generator transfer set-ups and would like some opinions....

What is better or more preferred by the pros?
A transfer panel that is set up like a sub panel
http://www.gen-tran.com/Merchant2/gr...01210_full.jpg

Or

A transfer switch that uses "Break/Make" switches for each circuit
http://ec1.images-amazon.com/images/...CLZZZZZZZ_.jpg

I'm leaning towards the panel but would like some professional input on both systems.
Thanks,
Phil
 
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  #2  
Old 03-11-06, 01:18 PM
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Join Date: Mar 2006
Posts: 13
transfer switch

Phil, I am a state licensed master electrician in Texas and I have designed and installed numerous genset/ATS projects and I will be glad to help you but I need to ask you some questions first to help me understand what you are trying to do.
1. Is this retrofitting an existing electrical service or is it all new?
2. If it is retofitting an existing and is a residence I need to know the details on your service. Such as size in amps - 100 or 200, whether your breaker box is inside or outside.
3. Is the generator going to be permantely mounted or a portable unit?
4. Did you want to supply generator power for your whole house or just essential loads I.E. 120 volt power to lights, refigerator, freezer & etc.
The two pictures you have on your posting are manual transfer switches and I personally prefer the automatic type. This is due somewhat to me being an electrician and I like anything that works automatically but in reality an ATS will sense when the normal side power is not available and will automatically start the genset and once the genset has reached the proper voltage and frequency will transfer over and power the loads until the normal power has been restored. This works best with a permanent mount genset but can work with a portable unit. Okay I have rambled enough. Let me know the answers to questions above and I will try to help you decide.

http://www.cutler-hammer.com/unsecur...A01602001E.PDF
I have the above link for you to go to if you like. This is for this company's residential light commercial ATS. I have one on my house and it works great and is a good fit for this market.
sruffin
 
  #3  
Old 03-11-06, 05:27 PM
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Originally Posted by sruffin
Phil, I am a state licensed master electrician in Texas and I have designed and installed numerous genset/ATS projects and I will be glad to help you but I need to ask you some questions first to help me understand what you are trying to do.
1. Is this retrofitting an existing electrical service or is it all new?
2. If it is retofitting an existing and is a residence I need to know the details on your service. Such as size in amps - 100 or 200, whether your breaker box is inside or outside.
3. Is the generator going to be permantely mounted or a portable unit?
4. Did you want to supply generator power for your whole house or just essential loads I.E. 120 volt power to lights, refigerator, freezer & etc.
The two pictures you have on your posting are manual transfer switches and I personally prefer the automatic type. This is due somewhat to me being an electrician and I like anything that works automatically but in reality an ATS will sense when the normal side power is not available and will automatically start the genset and once the genset has reached the proper voltage and frequency will transfer over and power the loads until the normal power has been restored. This works best with a permanent mount genset but can work with a portable unit. Okay I have rambled enough. Let me know the answers to questions above and I will try to help you decide.

http://www.cutler-hammer.com/unsecur...A01602001E.PDF
I have the above link for you to go to if you like. This is for this company's residential light commercial ATS. I have one on my house and it works great and is a good fit for this market.
sruffin
sruffin,
This will be retrofitted into an existing electrical service. The house is small at 1100 sq. ft. and had a fused service but the service has been updated within the last year. I think the new box is a 100 amp service. There is only one 220v, 30 amp breaker for the outdoor 2-ton condensing unit. There are 10 other circuits at 110v; most of them are 15 amp breakers except for two which are 20 amp breakers (one for the dishwasher and the other for the refrigerator.) We have a gas range, gas water heater and no well or sump-pump.

The breaker box is in the basement; the generator is a Generac 5000 watt portable. I plan on having the transfer panel mounted next to the existing service and hardwired to a receptacle in the garage (near the door.) That's where I will hook up the generator when needed. We don't get too many power outages; I just want to be prepared when/if they do happen.

I don't think my 5000 watt generator is enough to run the A/C condensing unit so I don't care to wire that to the transfer switch. I would like to be able to run all the other circuits (not together) but alternate them as needed so as to not overload the generator.

I'm not interested in an "automatic" transfer switch, mainly because of cost but also because we don't have outages that often. My generator will be sitting in the garage on wheels. When an outage occurs, I plan to wheel it outside the garage, fire it up, hook it up to the receptacle in the garage and transfer power from the utility to the generator via the transfer panel.
Thanks for your help!
Phil
 
  #4  
Old 03-11-06, 07:50 PM
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Join Date: Mar 2006
Posts: 13
transfer switch

Phil, Now that I know your application I would recommend going with the first transfer panel you have the picture of. The top two breakers which are for connection of normal power and emergency have a mechanical interlock between the trip handles that is called a walking beam. This assures that only one can be on at a time. For your service if the existing breaker panel has a 100 amp main circuit breaker in it then this will need to be what size goes in the transfer panel if you are planning on replacing the existing breaker panel entirely which is what I would do. If not then there will need to be a two pole circuit breaker added to power the transfer panel from the existing. This really does not make a whole lot of sense because you would have to move the 10 - 120 volt circuits over to the transfer panel and all that would be in the existing is the two pole for your AC and the two pole subfeed breaker. If you decide to go this route then I would make the subfeed a 60 amp 2 pole and install #6 copper conductors over to the normal power breaker in the transfer panel. I would install a #6 copper conductor for the neutral as well.
If you do decide to replace the existing entirely then you need to make sure that the transfer panel has a service entrance rating. This should be in the mfg. literature. If it does not have this rating then you will have to use it as a subfeed only. If you can use it then make sure the normal power circuit breaker matches your existing main circuit breaker in size.
On the genset side your 5 KW is good for 20 amps at 240 volts. This means that both phases can have 20 amps on them. Of course try to balance the 120 volt loads on each phase but this is not critical. I would size the emergency circuit breaker at 30 amps and install 4 #10 copper conductors from this circuit breaker to the receptacle. Two of the four are for the two hot phases, one is neutral and one is equipment ground. If you use non-metallic sheathed cable (romex) then a 10-3 with a ground can be used. If you end up going with the transfer panel as a subfed or feeder panel it will need to have a seperate neutral and ground bar installed in it and the neutral bar will need to be isolated. The #10 neutral will go to the neutral bar and the #10 bare ground wire will go to the ground bar. If you go with replacing the existing with a transfer panel with service entrance rating then there will only be one neutral/ground bar in it and both the #10 neutral and ground will connect to this.
I hope this is not to confusing but it is very critical that the neutral/ground connections are made correctly.
As far as running your condensor off of this 5 KW I am afraid you are right that it is not big enough. As stated above your 5 KW is good for 20 amps at 240 volts and that is probably pretty close to the current draw of your condensor and fan motor. I have found that there are a lot of different ways to calculate the genset sizing for inductive loads which is what all motors are and I have more or less settled on using a multiplier that is 2-3 times the KVA of the load. As an example lets take your AC unit. Lets say that the nameplate rating in current for your compressor and condensor fan motor is 20 amps combined. 20 amps times 240 volts = 4800 VA or 4.8 KVA (KVA is apparent power and power factor is not used in formula). 4.8 KVA x 2 - 9.6, 4.8 KVA x 2.5 = 12 KVA and times 3 = 14.4 KVA. All generators have a starting KVA rating. (The reason I am not using KW above is because KW is based on real power which you have to know the power factor of the motors which is not indicated on the nameplates anywhere. Genset sizes are indicated in KW because the mfg. know the power factor of the alternator). Your 5 KW probably has a KVA rating of 6.25 due to the power factor on most alternators is a .80. If you were to sale your 5 KW and got to a 10 or 12 KW it should be able to handle the starting KVA of your condensor and would handle the current draw fine once the condensor motors have got past startup. The main concern when starting a motor on a generator is if it is going to stumble the engine so bad that it stops running or dips the voltage to a very low level.
I have a 15 KW genset that turns at 3600 RPM. Your 5 KW should be the same. I have a 5 ton condensor with an all electric house which is why I have a 15 KW. The combined nameplate rating of my compressor and condensor fan motor is 36 amps. This times 240 volts = 8.640 KVA. This times 2 = 17.280 KVA. You can only buy either a 15 or 20 KW genset so I settled on a 15 KW for monetary purposes. When I start my condensor off generator power it does not effect it hardly at all which totally surprised me. I thought it would hammer the engine but that it would overcome it and go on. I have talked to some genset people and they theorize that because my unit is turning at 3600 RPM that the inertia from this is why my unit does not stumble. This is why I like using the 2-3 times multiplier.
You stated that your breaker panel is in your basement so I am guessing you live in the north or midwest or where hurricanes are not an issue. We went through hurricane Rita here last fall and with the 100 degree heat during the days and our power being off for one week the main thing I learned was that if you have a generator it has to be large enough to run your AC unit. Nothing else matters.
I hope this helps you and does not confuse you to much.
if you need any more info let me know.
sruffin
 
  #5  
Old 03-13-06, 03:58 AM
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Originally Posted by sruffin
You stated that your breaker panel is in your basement so I am guessing you live in the north or midwest or where hurricanes are not an issue. We went through hurricane Rita here last fall and with the 100 degree heat during the days and our power being off for one week the main thing I learned was that if you have a generator it has to be large enough to run your AC unit. Nothing else matters.
I hope this helps you and does not confuse you to much.
if you need any more info let me know.
sruffin
sruffin,
Yes, I'm in Michigan so no hurricanes but we do have Tornado warning this morning and they've been know to knock out a utility pole or two!

Anyway, thanks for the wealth of information. It is a great help! Just so you know, I'm not doing this job myself, I'm hiring an electrician but I want as much knowledge about transfer switches before the job is started.

I think I've decided to use a transfer panel (as a sub panel) but I'm only going to use either six or eight of the ten 120v circuits in my existing service. I think this will easily handle most of my needs during a power outage here in Michigan and shouldn't overload my generator.
Phil
 
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