generator and transfer switch install

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srvrrmguy

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This is my first post, I've enjoyed reading some of the archives and current posts. I guess any time a group of tradesmen get together to disscuss the problems and sollutions that we run into everyday can't be bad.
The question I have concerns installing astandby generator and transfer switch. If it is installed in same area as meter can w/ cb and the generator is installed outside, how many service disconnect switches are needed? The switch feeds a main lug panel of the same rating of cb located in meter can and above the cb on the generator.
thanks Eric
 
Re: generator and transfer switch install

The ATS should be protected from both sides. If the main disconnect is close to the Ats then it is only necessar to install one on the exit end of the ATS.
 
Re: generator and transfer switch install

Thanks for the input, I figured if the main cb was within los that would be the case. Are you saying that I need a disconnect on the load side of the switch? What about on the supply from gen set if its located out side of the room the switch is in. thanks again for your thoughts. Eric
 
Re: generator and transfer switch install

All three sides of the ATS must be protected for servicing purposes. If the load side of the ATS is terminated at the lugs in the panel then the panel will be live at all times, therefore there must be a disconnect before the lugs. One thing you didnt mention is this switch automatic or manual.

I hope I do understand your situation correctly.
 
Re: generator and transfer switch install

Originally posted by bajan:
All three sides of the ATS must be protected for servicing purposes. If the load side of the ATS is terminated at the lugs in the panel then the panel will be live at all times, therefore there must be a disconnect before the lugs.
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Bajan, there is no code reference that I know of to go with your statement.

There are service rated transfer switches that take the place of the service disconnect, they will be live unless the power company stops supplying power and the generator is off.

Bob
 
Re: generator and transfer switch install

Hi Bob
When a panel is fed to the lugs the panel is deemed to be live at all times. All ATS' are to have a disconnect so that they can be serviced or replaced by a qualified technician without the help of the power comany. In Barbados all supplies are to have a disconnect next to the meter in case of emergency as well as at the main panel. I see it as a basic safety precaution. If there is a major overload in the system then the ATS will be responsible for the shut down, because there is no Breaker controlling the main panel.
 
Re: generator and transfer switch install

thanks for the input guys. The transfer switch in this installation will be protected by the main breaker located in meter can. Why would you need the disconnect on the load side of the ats?
The switch is automatic and the job may be cancelled as the customer is out grown current location. thats good as it will mean more work in the long run. eric
 
Re: generator and transfer switch install

The generator circuit is a feeder, not a service. The service disconnect protects the wiring, transfer switch and main panel while fed from the utility. The generator disconnect protects the emergency side. Having both disconnects locked open protects the personnel during maintenance of the main swbd and/or transfer switch.

Relative distances do not matter.

[ July 15, 2004, 11:08 PM: Message edited by: sparkie001 ]
 
Re: generator and transfer switch install

Originally posted by bajan:
Hi Bob
When a panel is fed to the lugs the panel is deemed to be live at all times.
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Not by NEC but maybe in your employer's practice.

All ATS' are to have a disconnect so that they can be serviced or replaced by a qualified technician without the help of the power comany.
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The building service disconnect does that.


If there is a major overload in the system then the ATS will be responsible for the shut down, because there is no Breaker controlling the main panel.
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The Service disconnect protects the panel.
 
Re: generator and transfer switch install

If you have a disconect at the service then the one on the generator I see no perpose for any disconect between the load side of a tranfer switch as the other two will render no voltage at the tranfer switch when maintance is preformed. If the generator is close (within sight) of the transfer switch it can serve as the disconect but also if the generator can also be made inoperatable by a on/off switch on it, it too will work. As a generator that cant run cant produce power.
 
Re: generator and transfer switch install

Originally posted by hurk27:
If the generator is close (within sight) of the transfer switch it can serve as the disconect
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What Code reference are you basing this statement on? A transfer switch is not a motor controller. It doesn't need a disconnect switch within sight.

also if the generator can also be made inoperatable by a on/off switch on it, it too will work
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I have never seen one of these switches being padlockable, so use of the genset on/off switch would not comply with lockout/tagout rules and would be dangerous.
 
Re: generator and transfer switch install

Ok how about this:

445.18 Disconnecting Means Required for Generators.
Generators shall be equipped with a disconnect by means of which the generator and all protective devices and control apparatus are able to be disconnected entirely from the circuits supplied by the generator except where:
(1) ""The driving means for the generator can be readily shut down;"" and
(2) The generator is not arranged to operate in parallel with another generator or other source of voltage.
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from (1) So if there is a switch that will not allow the engine to run then it's allowed.

[ July 16, 2004, 02:55 AM: Message edited by: hurk27 ]
 
Re: generator and transfer switch install

Generally, depending on the size and voltage of the generator, it comes with a breaker.
Most often than not there is a breaker from the Normal to the ATS, From the Generator to the ATS and from the ATS to the load (main breaker on panel). This is a means to isolate, but I have seen instances with out all these disconnects and an RMTD type bypass/isolation switch has been used.
You never mentioned the type of Emergency system this was? Fire Pump, Life Safety, etc. That can make a difference.
You never mentioned the size of the generator/ATS or Panel.
Good practice is to include a breaker for each side of the ATS for people that will be working the switch later and No you cannot rely on stopping the engine, that is only 1/2 the equation.
By adding 3 breakers, the utility does not need to be involved, unless you have huge demand charges for outages (depending on utility contract).
When designing, sit back and ask yourself how would you replace contacts on the ATS in a year safely and that should provide you with an answer.
 
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