transfer switch as service disconnect

[izak]

I know that this may have been covered before, in some way, but here is my situation:

I am to install a 400 amp single phase service on a commercial building
the customer wants a transfer switch and will be setting a permanent generator.

I am planning to install a full size (400a) transfer switch

Due to space restrictions, I am hoping to use the transfer switch as the service disconnect, and install a main breaker panel close to it. (by close, I mean within 10 feet on the same wall. Definitely within sight)

the transfer switches that I have been quoted are shown as 'service equipment', however, our state inspector indicated to me (in a brief conversation) that I needed to set a disconnect ahead of the transfer switch

I have found several references on line showing a transfer used as service disco when installed 'immediately adjacent' to a main breaker panel
however none of it cited any code sections.

would anyone be willing to cite me the appropriate code sections (2005, 2008 or 2011) that apply to this situation?
Also any additional advice would be great. Im designing this on the fly and dont want to miss anything

thank you

Isaac

 

[texie]

I know that this may have been covered before, in some way, but here is my situation:

I am to install a 400 amp single phase service on a commercial building
the customer wants a transfer switch and will be setting a permanent generator.

I am planning to install a full size (400a) transfer switch

Due to space restrictions, I am hoping to use the transfer switch as the service disconnect, and install a main breaker panel close to it. (by close, I mean within 10 feet on the same wall. Definitely within sight)

the transfer switches that I have been quoted are shown as 'service equipment', however, our state inspector indicated to me (in a brief conversation) that I needed to set a disconnect ahead of the transfer switch

I have found several references on line showing a transfer used as service disco when installed 'immediately adjacent' to a main breaker panel
however none of it cited any code sections.

would anyone be willing to cite me the appropriate code sections (2005, 2008 or 2011) that apply to this situation?
Also any additional advice would be great. Im designing this on the fly and dont want to miss anything

thank you

Isaac

If you use a SUSE rated ATS you don't need a main breaker in front of or after the ATS. The load side is now a feeder and you can continue that to where ever your MLO panel is, even inside.

 

[raider1]

Provided that the ATS is listed as suitable for service equipment then the overcurrent protective device can be installed immediately adjacent to the service disconnecting means (ATS) Check out 230.91.

Now the definition of immediately adjacent thereto may be up for discussion as far as having the main breaker panel located 10 feet from the ATS.

Chris

 

[xxmrwhitexx]

Wouldn't the OCPD need to be installed ahead of the "normal "line side of the ATS? I am pretty sure when the service entrance rated transfer switches are furnished with an integral main circuit breaker, it is configured that way.

 

[texie]

Provided that the ATS is listed as suitable for service equipment then the overcurrent protective device can be installed immediately adjacent to the service disconnecting means (ATS) Check out 230.91.

Now the definition of immediately adjacent thereto may be up for discussion as far as having the main breaker panel located 10 feet from the ATS.

Chris

I would agree if this was a manual transfer SUSE rated switch with no OC protection integral to the switch ( they do make them). But I think the OP is refering to an automatic SUSE rated transfer switch, which in my experience are only available with a main breaker that is the main disconnect/OC for the service. No other MOCP is required in this case either before or after the ATS.
To the OP: If you have a ATS SUSE rated with a main, the inspector is mistaken about needing a main ahead of the switch. You can do it just as I described in my post 2.

 

[raider1]

I would agree if this was a manual transfer SUSE rated switch with no OC protection integral to the switch ( they do make them). But I think the OP is refering to an automatic SUSE rated transfer switch, which in my experience are only available with a main breaker that is the main disconnect/OC for the service. No other MOCP is required in this case either before or after the ATS.
To the OP: If you have a ATS SUSE rated with a main, the inspector is mistaken about needing a main ahead of the switch. You can do it just as I described in my post 2.

Your correct, I was thinking manual transfer switch not automatic.

Chris

 

[charlie b]

The tricky part is that the ATS probably gets its normal feed from a transformer. It is allowable to run a secondary conductor from a transformer into a building, without putting an OCPD right at the transformer itself. But there are restrictions. One of them is that the first thing that the secondary conductor hits must be an OCPD. You can't go from the transformer to the ATS and then to the main switchboard, with the first OCPD being the main breaker on the main switchboard. And it would not matter if the transfer switch were manual or automatic. Reference 240.21(C)(2)(2) and 240.21(C)(4)(2). I find it entertaining that the wording of 240.21(C)(3)(2) is different enough that the same requirement (i.e., hit the OCPD first) might not be in play.

 

[izak]

manual

manual

actually I was referring to a MANUAL Transfer switch

and Im sorry that I didnt clarify

Square D quoted me a Service Equipment rated Manual Transfer Switch

why else would it be rated for Service Equipment if I cannot use it as a Disconnect?

Isaac

 

[GoldDigger]

actually I was referring to a MANUAL Transfer switch

and Im sorry that I didnt clarify

Square D quoted me a Service Equipment rated Manual Transfer Switch

why else would it be rated for Service Equipment if I cannot use it as a Disconnect?

Isaac

One possible concern the inspector may have is that a manual transfer switch will close the connection to the alternate power source at the same time it opens the POCO side. There is no way to disconnect from both without a separate disconnect for one source or the other.

 

[charlie b]

You can have a manual transfer switch with a "center-off" position. In that position, it would serve as a disconnecting means. "Service-rated" also tells you that that is the place to bond the neutral and ground wires together, and run EGCs to everything downstream.

Please note, however, that there are two separate requirements, and what you are describing only takes care of one of them. The building needs a disconnecting means; you have that. Both the wire from the generator and the other wire from the utility transformer need overcurrent protection. You don't get that from a MTS, unless it includes a breaker on the line side.

 

[ceb58]

actually I was referring to a MANUAL Transfer switch

and Im sorry that I didnt clarify

Square D quoted me a Service Equipment rated Manual Transfer Switch

why else would it be rated for Service Equipment if I cannot use it as a Disconnect?

Isaac

You need to go back to post # 3. You can use the switch but the OCP must be ether part of the disconnect or immediately adjacent thereto. Your main panel 10 ft away may not impress the inspector.

 

[texie]

actually I was referring to a MANUAL Transfer switch

and Im sorry that I didnt clarify

Square D quoted me a Service Equipment rated Manual Transfer Switch

why else would it be rated for Service Equipment if I cannot use it as a Disconnect?

Isaac

Well, the devil is in the details. Just because it is service rated that does not necessarily mean it has overcurrent protection and can be used as the service disconnect. For example, a meter socket is service rated but it is not a service disconnect. You could however get a service rated FUSIBLE double throw, center off safety switch and use that as your manual transfer switch and service disconnect.