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Old 04-18-2009, 06:30 PM   #1
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Potentially overloading Service??


I could use a little insight on this...

I have a 200A service feeding a transfer switch (non-fused). The transfer switch then feeds (2) 200A panels (one for the house, one for the shop). The meter, transfer switch and taps are all made remotely in a small outbuilding dedicated to the electrical equipment.

Is this acceptable? I have seen several installations that are similar, where the service is tapped & connected disconnect switches (ultimately sub-panels) with additive ratings higher than the feeder rating.

Thanks for any thoughts you may have.

David

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Old 04-18-2009, 06:59 PM   #2
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Potentially overloading Service??


Is there a Main breaker or shut off switch?

You can have as many feeds as you want so long as there is a 200a Main protection somewhere

If there isn't then it is possible to draw more power then the service feed can handle. Have you done a power calc to figure out how much power you are drawing normally? I have a 200a service & my calc comes in around 143a

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Old 04-18-2009, 07:36 PM   #3
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Potentially overloading Service??


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.

Is this acceptable? I have seen several installations that are similar, where the service is tapped & connected disconnect switches (ultimately sub-panels) with additive ratings higher than the feeder rating.
that is actually typical. If you add all the breakers in most panels, the total will exceed the panels rating.

as dave said, is there a main breaker?

after that, are there breakers for the subs and if so, what size and what size wire is feeding them?
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Old 04-18-2009, 08:16 PM   #4
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Potentially overloading Service??


Just as an FYI, I have 800a of breakers in my main panel + 315a in subs - so far

Melting the feed wires is unlikely - but it has happened
As has transformers going up
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Old 04-18-2009, 08:29 PM   #5
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Potentially overloading Service??


Thanks for the replys... in response for more info.

There is no over current protection on the service.

XFMR > Meter > Xfer Switch > Tap to 200A panel A (house)
> Tap to 200A panel B (feeding 3 smaller sub panels)

The Transfer Switch does provide a disconnect means, but no over current protection.

4/0 wiring feeds the transfer switch. 4/0 wiring to both panel A & B.

No issues with the mains and branch circuits in panels A & B... they are well coordinated. I don't expect to ever approach the capacity of the service with all loads combined, but my concern is that in theory, the service could easily be overloaded if one didn't plan properly. Do the tap rules allow you to do this legally?

Thanks
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Old 04-18-2009, 08:57 PM   #6
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Potentially overloading Service??


yes, you do have a problem then. You could theoretically draw 400 amps on the service feeders. Your transfer switch needs to be rated for the 400 amps or greater and your meter must be at least a 320 amp meter. The feeders from the utility drop to where ever the panel feeds split off must be rated for the 400 amps. What the POCO does is beyond human review so the service lateral is irrelevent.


and tap rules? what tap rules are you referring to, specifically, that you believe may apply. Without looking, any tap rule I can think of would require OCPD for the main service feeders.

Who approved this installation?
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Old 04-19-2009, 06:27 AM   #7
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Potentially overloading Service??


Thanks...

This is an inherited installation... I'm working to correct it before moving in. If a set of 200A fuses (or a 200A breaker) were installed in front of the transfer switch (immediately after the meter), that should provide proper over current protection for the service feeders... correct?

Thanks for your time and thoughts.
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Old 04-19-2009, 08:33 AM   #8
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Potentially overloading Service??


Quote:
Originally Posted by dgajr View Post
Thanks...

This is an inherited installation... I'm working to correct it before moving in. If a set of 200A fuses (or a 200A breaker) were installed in front of the transfer switch (immediately after the meter), that should provide proper over current protection for the service feeders... correct?

Thanks for your time and thoughts.
Yes. That would work.
I don't see any tap rule being allowed here.
The tap rules are 10' and 25"
Even though you have two 200 amp panels ( I assume you have main breakers in them) you will be limited to the main feed of 200 amps.

What you need is this.
meter > fused or breaker disconnect > transfer switch(with two lugs to feed the panels) > panels
How is the tap made in the transfer switch?
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Old 04-19-2009, 11:16 AM   #9
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Potentially overloading Service??


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If a set of 200A fuses (or a 200A breaker) were installed in front of the transfer switch (immediately after the meter), that should provide proper over current protection for the service feeders... correct?
yes but the question now becomes; do the 2 200 amp panels combined draw over 200 amps at any time. Obviously, they could conceivably do so so the best fix would be to install a 400 (320 resi) meter, feeders and 400 amp transfer switch to remove the possibility;

or;

you could simply install the 200 amp main and if/when it trips, upgrade to the 400 amp stuff.

Don't think because you haven't had a meltdown yet means you are drawing less than 200 amps total. Depending on the wires and the installation, you could have gone beyond that and not necessarily had any noticeable damage.

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