DISCONNECT ON UTILITY SIDE OF AN ATS
DISCONNECT ON UTILITY SIDE OF AN ATS
(OP)
I have been trying to determine the NEC code requirement of a disconnect switch on the "utility" side of an automatic transfer switch. This is for a 701 legally required standby system with diesel generator as back-up source. I note that the handbook drawing of exhibit 700.1 does not indicate one (sorry, but drawings are "sometimes" worth a thousand words:). My feeling is that there should be one to isolate the switch for maintenence. However would it be legal to instead use pole mounted fused disconnects on the primary side of the transformer? for a new design I would put one in, but in this case the construction is already started and I would prefer to not to introduce a mod unless it is strongly suggested.
Thanks and be nice.
Thanks and be nice.






RE: DISCONNECT ON UTILITY SIDE OF AN ATS
The only exception I can think of is if the ATS is service-entrance rated, which means that it serves as its own disconnect, and generally implies that it is a two-breaker transfer switch.
There's no requirement for a LOCAL disconnect at an ATS.
Keep in mind that you'll usually have, at minimum, a utility disconnect, and in 99% of installations you'll have downstream distribution too. And your feeders to the ATS all require overcurrent protection per Article 240. And your generator requires overcurrent protection unless it's self-protecting (which is rare). And 701.6 requires that your entire emergency system have adequate capacity. Put all that together, and there's no way you could come to the conclusion that a disconnect is not required for the ATS.
And if you're still not convinced, see 230.82(4), which requires that even if you tap ahead of the service disconnect, you gotta provide another service disconnect.
230.70 requires that the disconnect be in a readily accessible location -- a pole mounted disconnect might or might not meet the Article 100 definition of "Accessible, Readily", it'd depend on the specifics of the installation (you definitely could not require a ladder to operate it).
Hope this helps.
RE: DISCONNECT ON UTILITY SIDE OF AN ATS
The ats is connected to this generator and a padmount transformer with OH fused cut-out protected primary lateral as well as the oil immersed primary fuses. On the transformer secondary side, currently there is no disconnects or fuses on the feed to the ats. The load side of the ats is tapped three ways feeding 3-buildings w/2 out of three having CB disconnects protecting these lower amperage feeds. The main building feed is not protected up to the main building CB disconnects. This was an interpretation of NEC 240.21 (5), outside taps of unlimited length.
Therefore I have met article 240 for conductor protection, primary conductors, secondary conductors and generator feed.
and I have met 230.82 by protecting the tapped feeders post ATS
I have met 230.70 by having readily accessible disconnects on the main and auxillary building's service entrances.
I am not saying this is a sound design practice, but nothing in the code I see yet says I can not do it. (A challenge to the code kings).
RE: DISCONNECT ON UTILITY SIDE OF AN ATS
RE: DISCONNECT ON UTILITY SIDE OF AN ATS
Why not just ask the local inspector for an interpretation and get it over with? You'll have to do it at some point.
RE: DISCONNECT ON UTILITY SIDE OF AN ATS
As for inspectors, this is on a federal reservation, there is no inspectors per say. The contractors are responsible to provide there own quality control contractor CQC that can offen double as a super. It interesting to note that the
CQC's job is at the mercy of the prime who can fire him and get another. Welcome to the wacky world of federal work.
RE: DISCONNECT ON UTILITY SIDE OF AN ATS
I was burned on this once and had to install a 400A fused disconnect ahead of the ATS as a change order so I feel your pain.
RE: DISCONNECT ON UTILITY SIDE OF AN ATS
The key thing is to get the service entrance rating. And yes, ASCO can provide such a rating.
I'd sort of already pointed this solution out to you: "The only exception I can think of is if the ATS is service-entrance rated, which means that it serves as its own disconnect, and generally implies that it is a two-breaker transfer switch."
RE: DISCONNECT ON UTILITY SIDE OF AN ATS
RE: DISCONNECT ON UTILITY SIDE OF AN ATS
RE: DISCONNECT ON UTILITY SIDE OF AN ATS
RE: DISCONNECT ON UTILITY SIDE OF AN ATS
And thanks, I like the idea of getting the switch with a service entrance rating, I will (try to) use this requirement to reject a non service entrance rated ats submittal.