Transfer switch requirements for residential standby generator

[JosephPrince]

I have installed a Cutler Hammer 20 KW natural gas powered standby generator in a residential home. The home has a 200 amp overhead electrical service with the electric meter on the outside of the house, and a 200 amp main breaker electric panelboard directly below in a basement. My installation consists of: transferring the complete 200 amp panel with a 200amp rated automatic transfer switch located outside. I have taken the feeders off the load side of the meter enclosure and installed them to the utility side of the transfer switch. I then rerouted the conduit from the meter enclosure to the transfer switch and installed new feeders from the load side of the transfer switch to the existing panelboard. The transfer switch does not have a service disconnect, and to understanding of the code does not require one. Others are disagreeing and suggesting I need a t/s with a service disconnect. If this is correct, then I must now take all neutral and grounds in the main panel and separate them. What code article would I reference? What is your input to this installation.

 

[infinity]

What is the connected load on this generator?

Welcome to the Forum.

 

[augie47]

In addition to addressing Robs question, you need to determine if the transfer switch is "service rated"... without main pvercurrent protective device it is probably not. Non-service rated TS are not among the items listed in 230.82 allowed ahead of your service disconnect.

 

[russ]

I have taken the feeders off the load side of the meter enclosure and installed them to the utility side of the transfer switch. I then rerouted the conduit from the meter enclosure to the transfer switch and installed new feeders from the load side of the transfer switch to the existing panelboard.

Not sure, but are you using the utility meter as part of the raceway for the feeder, from the transfer switch, to the breaker panel.

230.7 Does not allow this

 

[ceb58]

I have installed a Cutler Hammer 20 KW natural gas powered standby generator in a residential home. The home has a 200 amp overhead electrical service with the electric meter on the outside of the house, and a 200 amp main breaker electric panelboard directly below in a basement. My installation consists of: transferring the complete 200 amp panel with a 200amp rated automatic transfer switch located outside. I have taken the feeders off the load side of the meter enclosure and installed them to the utility side of the transfer switch. I then rerouted the conduit from the meter enclosure to the transfer switch and installed new feeders from the load side of the transfer switch to the existing panelboard. The transfer switch does not have a service disconnect, and to understanding of the code does not require one. Others are disagreeing and suggesting I need a t/s with a service disconnect. If this is correct, then I must now take all neutral and grounds in the main panel and separate them. What code article would I reference? What is your input to this installation.

Since your ATS is not SE rated then yes you must have a disconnect between the meter and ATS 225.31 & 225.36. You will also need to install a disconnect for the gen. feed. Chances are the C-H (Generac) breaker will not/dose not meet 445.18, 225.36 and 702.11 and you must meet 225.31.
If you are under 2008 code you must meet 702.5 (2) (a)(b) as far as load is concerned

 

[ceb58]

Not sure, but are you using the utility meter as part of the raceway for the feeder, from the transfer switch, to the breaker panel.

230.7 Does not allow this

Good catch. From the OP description it sound like this is what was done.
Also the load rateing of the Gen. will change

I have installed a Cutler Hammer 20 KW natural gas powered

The unit is sold as a 20kw but running on natural gas it cuts it back to around a 18kw. The only way to get the 20kw rating would be to run it on LP gas.

 

[tom baker]

if you are under the 2008 NEC, a change in Article 702 requires that your system, with an ATS, be sized to carry the entire calculated load, thats probably not 200A but could be 24KW or more.

 

[Smart $]

if you are under the 2008 NEC, a change in Article 702 requires that your system, with an ATS, be sized to carry the entire calculated load, thats probably not 200A but could be 24KW or more.

You are referring to 702.5(B)(2)(a). Employing a load management system under condition (b) therewith permits a lesser-rated generator to be used.

 

[tryinghard]

...The home has a 200 amp overhead electrical service...and a 200 amp main breaker electric panelboard directly below in a basement. My installation consists of: transferring the complete 200 amp panel with a 200amp rated automatic transfer switch located outside.

What size overcurrent protection device (breaker) does the 20kw have? How will this adequately supply the home that currently has 200A capacity?

 

[ceb58]

What size overcurrent protection device (breaker) does the 20kw have? How will this adequately supply the home that currently has 200A capacity?

A 20kw will usually have a 100amp breaker. The 20kw would convert to around 83amps then using the next size larger it would be 100. But as I said the OP is hooking it to NG which would bring it down to around 75amps

 

[Smart $]

What size overcurrent protection device (breaker) does the 20kw have? How will this adequately supply the home that currently has 200A capacity?

A 20kw will usually have a 100amp breaker. The 20kw would convert to around 83amps then using the next size larger it would be 100. But as I said the OP is hooking it to NG which would bring it down to around 75amps

That 75A is a max' continuous rating. It can supply a calculated load up to 94A (i.e. a calculated load factors continuous loads at 125%).

The service load will need to be calculated, in order to determine whether load management is required... or to circumvent load management by installing a standby power subpanel.

Also, just because a service is 200A does not mean a 200A is required. I can have a calculated load of 50A and install a 200A-rated service if I want.

 

[tryinghard]

That 75A is a max' continuous rating. It can supply a calculated load up to 94A (i.e. a calculated load factors continuous loads at 125%).

The service load will need to be calculated, in order to determine whether load management is required... or to circumvent load management by installing a standby power subpanel.

Also, just because a service is 200A does not mean a 200A is required. I can have a calculated load of 50A and install a 200A-rated service if I want.

I know this but the reasoning is inconsistant; 200A wanted/needed for home except if gen set then do whatever? Calculating a acceptable OCPD for a gen set may not be whats exacty in the unit, point is this case for sure, it's not the same as the whole residence it supplying. They could design load control through a sub panel arrangement.

 

[iwire]

I know this but the reasoning is inconsistant; 200A wanted/needed for home except if gen set then do whatever? Calculating a acceptable OCPD for a gen set may not be whats exacty in the unit, point is this case for sure, it's not the same as the whole residence it supplying. They could design load control through a sub panel arrangement.

The point was that there is no reason at all to assume that a home with a 200 amp service actuality has a calculated load above 94 amps continuous.

 

[tryinghard]

The point was that there is no reason at all to assume that a home with a 200 amp service actuality has a calculated load above 94 amps continuous.

That's for sure and this same assumption should not alow any size gen set [grin]; just calc it and run with a supported decision.