Adding ATS to existing service

[George Stolz]

Via PM:

hi George
I am looking for information that gives a choice on wiring of a whole house transfer switch. service rated.
Do you have the option to wire as a sub panel and leave the service panel wired as the main (remain the same) even though the service wires come to the transfer switch first.
I am asking because I thought I saw that discussion on q&a or possibly a newsletter a while back.
Any suggestions?

john parish

 

[GoldDigger]

IMHO any panel that the service wires enter without earlier OCPD needs to be service rated.
If the unprotected service wires come straight to an ATS or MTS, the transfer switch itself must be service rated.
If the transfer is done via an interlocked main and backfed breaker, the main and panel need to be service rated.
Where to put the ground/neutral bond is a separate question.

 

[iwire]

Here is how I see it, section '230.82 Equipment Connected to the Supply Side of Service Disconnect' prohibits connecting an ATS on the supply side of the service disconnect.

That being the case I see two options for a whole house transfer switch.

1) Add a new service rated fused or breaker disconnect to become the new service disconnect, connect that to any transfer switch and on to the original panel

OR

2) Use a service rated transfer switch and feed the existing panel from there.


However, with wither of those the panel inside must become a sub panel with an isolated neutral bar, separate grounding bar, the GEC may have to be relocated to the new service disconnect. If the panel is an old one it may not even be designed to have an isolated neutral.

Of course you will need a four wire feeder between the new service disconnect and this subpanel.


Price the job accordingly.

 

[ActionDave]

Most of the transfer switches I have installed have been after the service disconnect. I don't know any real good reason to replace an existing service disconnect with a service rated transfer switch other than the existing service is obsolete.

 

[ceb58]

I am looking for information that gives a choice on wiring of a whole house transfer switch. service rated.
Do you have the option to wire as a sub panel and leave the service panel wired as the main (remain the same) even though the service wires come to the transfer switch first.

If the, as you call it, the service panel is left then you must first start with 702.4(2). Is the generator capable of handling the full calculated load or are you going to incorporate load shedding to comply? If the generator will handle the connected load then the "main" panel now becomes a sub panel because your SE rated ATS is now your first service disconnect/overcurrent device. There must now be 4 wire ran to the panel with the neutrals and grounds separated and isolated along with changing the location of the grounding electrode conductor to the ATS ( unless it is bonded to the neutral in the meter base)