Tap rule help

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majik009

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Massachusetts
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Electrical Contractor
Hi all, and good day ....
Been reading the forum for years, and cant thank you all enough for the valuable information that everyone shares here !!

My question is
I have a commercial modular metering tap question (GE mini mod ll) circa 1980s
We need to add a 4 high stack to an existing installation
The existing is in a small electrical room, with a main service circuit breaker disconnect bottom fed from an underground utility conduit, and in turn feeds out overhead via pipe and wire to the tap box on a opposite wall, and the meter stacks with tenant mains extend both left and right of the center tap box
Because of space and compatibility constraints we cannot simply bolt up another stack to the existing
We will still locate that in the electrical room but a little away from the meter packs are now
My question is - if we extend the tap from the existing tap box - will we need overcurrent protection at the new stack location
Or will we need to tap from the main breaker and still possibly need OCP at the new stack ?

Thanks

Bob
 
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petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
majik009 said:
My question is - if we extend the tap from the existing tap box - will we need overcurrent protection at the new stack location
Click to expand...

The answer is to be found in the definition of a tap. It has to terminate at an OCPD, so the answer to your question is that if it is a tap, than you have to terminate it at an OCPD.

OTOH, if you are just extending the wires from the load side of the OCPD the original tap terminates at, and the wires are adequately protected by that OCPD, the extension is not actually a tap.
 
augie47

augie47

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Tennessee
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State Electrical Inspector (Retired)
Bob, am I misreading or will the 10ft tap rule not allow you to terminate in equipment with deviceS not exceeding the ampacity (no main) ?
 
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petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
augie47 said:
Bob, am I misreading or will the 10ft tap rule not allow you to terminate in equipment with deviceS not exceeding the ampacity (no main) ?
Click to expand...
it depends on whether it is a tap or not. a tap has to terminate at an OCPD. If the conductor is fully protected by an upstream OCPD, it is not actually a tap.

A tap also cannot use the 6 handle rule. It has to terminate at a single OCPD.
 
electrofelon

electrofelon

Senior Member
Location
Cherry Valley NY, Seattle, WA
petersonra said:
it depends on whether it is a tap or not. a tap has to terminate at an OCPD. If the conductor is fully protected by an upstream OCPD, it is not actually a tap.

A tap also cannot use the 6 handle rule. It has to terminate at a single OCPD.
Click to expand...

I think I have to disagree there, due to that dreadful wording in the 10' tap rule. IT does seem to allow for a tap to terminate on "main lugs" and since a meter stack is not a panelboard, I dont see 408.36 applying. That said, it appears the ampacity of the tap would have to be equal to or greater than the bus rating of the meter stack. I just did one rated 500 amps, so that would make it unlikely that it could be supplied by a tap.

So in short, I would say the OP would just extend the feeder to the new meter stack and call it a day (assuming calcs work out).
 
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nickelec

Senior Member
Location
US
Maybe I'm wrong but I'm pretty sure tap rules do not apply for services?

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nickelec

Senior Member
Location
US
Coming back to this on a separate set up

1200 amp buss fed breaker

Load side -3 sets of 500 kcmill feeding there individual 400 a MBPs

The next size up rule does not apply to circuits 800a or more does this apply to load or line side of the breaker .

I'm pretty sure the above set up is compliant

This is also not a service

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electrofelon

electrofelon

Senior Member
Location
Cherry Valley NY, Seattle, WA
nickelec said:
Coming back to this on a separate set up

1200 amp buss fed breaker

Load side -3 sets of 500 kcmill feeding there individual 400 a MBPs

The next size up rule does not apply to circuits 800a or more does this apply to load or line side of the breaker .

I'm pretty sure the above set up is compliant

This is also not a service

Sent from my SM-G986U using Tapatalk
Click to expand...
Ok for a 10 foot tap, not compliant for a 25' tap.
 
david luchini

david luchini

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Location
Connecticut
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Engineer
nickelec said:
Coming back to this on a separate set up

1200 amp buss fed breaker

Load side -3 sets of 500 kcmill feeding there individual 400 a MBPs

The next size up rule does not apply to circuits 800a or more does this apply to load or line side of the breaker .

I'm pretty sure the above set up is compliant

This is also not a service

Sent from my SM-G986U using Tapatalk
Click to expand...
Not compliant. You have 3 sets of tap conductors (500kcmil) to 400A c/bs. The ampacity of the 500kcmil is too low.
 
david luchini

david luchini

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Connecticut
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Engineer
nickelec said:
To low because if the 800a or more rule?

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Click to expand...
It's low because of the tap rule.

If it was supplying a single piece of equipment, it would be low because its the ocpd is over 800A. (It's "more than 800A", not "800A or more".)
 
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nickelec

Senior Member
Location
US
So the over 800 amp rule applies here also ? That's what I'm confused about

Is it not compliant because of both rules

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david luchini

david luchini

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Location
Connecticut
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Engineer
nickelec said:
So the over 800 amp rule applies here also ? That's what I'm confused about

Is it not compliant because of both rules

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Click to expand...
I don't think the over 800A rule applies. The conductors are tap conductors, the 1200A c/b isn't providing overcurrent protection for them.
 
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