Bus Tap question.....

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Fulthrotl

Fulthrotl

~Autocorrect is My Worst Enema.~
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HB, CA (19 Hrs. 22 Min. from Winged Horses)
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E
ok, i had a plan, that did not survive contact with the AHJ.
expedited plan check, and less than an hour after taking my
money, my engineered wet ink signed drawings were smoked.

fooey.

this is all for a silly temp power panel for a project i'm wiring.

here was my plan:

mount a 100 amp 480 volt fused disconnect behind the main gear,
feed it using the 10 foot tap rule off an unused 800 amp main breaker,
with #2 thhn less than 10 feet long.

then go from the disconnect 30' in schedule 80, to a 75 kva xfmr, with
a 200 amp 3 phase 4 wire 120/208 volt panel mounted next to it.
sit the transformer up on a plastic support pad, so it's off the dirt.

put some 20 amp gfci devices in bell boxes next to the panel, and then
everyone can plug in their stuff for power and charging batteries, etc.

AHJ won't allow me to just hit the bottom of that 800 amp breaker.
requires i tap the bus above the breaker. before i do that, does anyone
know of or have used a clamp to hit the bus without drilling? i've used them
in trade shows to tap off main busbars in gear, but i've not seen anything
like that available.

i was given this other option to use the breaker.......

put in a 400 amp 3 phase fused disconnect, with reducers to 100 amp,
and feed it off the breaker with parallel 500 mcm copper.

anyone got suggestions for a solution?
 
no solution at the moment, but a question. what is the reasoning for not allowing the tap off the breaker ?
 
It looks like to meet the 10' tap rule why wont they allow it? Did they give you a reason?

If I understand you correctly, they want you to tap a hot bus instead of the load side of the 800A ocpd?
 
Your tap complies with 240.21(B)1, so why not fight it?

I would really love to hear the AHJ's reasoning behind wanting a tap ahead of the breaker rather than after it.
 
Cow said:
Your tap complies with 240.21(B)1, so why not fight it?

I would really love to hear the AHJ's reasoning behind wanting a tap ahead of the breaker rather than after it.
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my EE looked funny when i said i wanted to do it that way, looked it up in the book,
and said it was ok by him.

i've learned to pick my battles. this isn't worth getting all wrapped about.

worst case, i have to hot tap the bus, or down the gear to do it cold.
if i have to down the gear, i'm gonna set off sprinkler and server and
burglar alarms for a few folks, and i'd rather not do that.

i'll take a peek inside the gear in the morning, and see what gives.
i'm sure a simple solution will present itself, and i can perform it in a
workmanlike and safe manner...

there were these really cool burndy clamps that you could hang on
a 1/4" bus, and tie stuff on.... but it's been a long time since i've seen any.
time to get creative.... if anyone has any flashes of inspiration, i'd like to hear them...

thanks.
 
edward said:
It looks like to meet the 10' tap rule why wont they allow it? Did they give you a reason?

If I understand you correctly, they want you to tap a hot bus instead of the load side of the 800A ocpd?
Click to expand...

yes. if i want to go off the load side of the 800 amp main, the AHJ wants parallell 500 mcm to a 400 amp switch,
with reducers to 100 amp fuse size. that will cost $3k in materials. screw that, before i'll piss that kind of money
away, i'll buy a 3kw honda generator, and two gas cans...

here's your plug.... pull this rope thingie here.....
 
Fulthrotl said:
his premise is that after the ocpd, it's not a tap, it's a feeder. before the ocpd, it's a tap.
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That idea is why I submitted the following for the 2011 code.
10-45 Log #4825 NEC-P10 Final Action: Reject
(240.21(B))
_______________________________________________________________
Submitter: Don Ganiere, Ottawa, IL
Recommendation: Add text to read as follows:
(B) Feeder Taps. Conductors shall be permitted to be tapped, without overcurrent protection at the tap, to a feeder as specified in 240.21(B)(1) through (B)(5). Feeder taps shall be permitted to originate at the load terminal of an overcurrent protective device. The provisions of 240.4(B) shall not be permitted for tap conductors.

Substantiation: This type of installation is permitted in many areas, but the code does not specifically permit it. The additional wording will make it clear that this is a code compliant installation. As long as all of the conditions of this section are complied with the point of origination of the tap conductor does not create any additional hazard.
Panel Meeting Action: Reject
Panel Statement: The proposed language is not necessary as the present language permits such installation where appropriate.
Number Eligible to Vote: 12
Ballot Results: Affirmative: 12
Click to expand...
 
So put "full size" conductors on the OCPD load terminals and then, possibly inside the same panel, reduce (with Polaris connectors) to your tap conductor size. I do not see how the inspector could argue with that. The tap would have to end on an OCPD of course.
 
Fulthrotl said:
his premise is that after the ocpd, it's not a tap, it's a feeder. before the ocpd, it's a tap.
Click to expand...

That's absurd. So by his logic if you put a 1 foot long conductor on the OCPD then connected your tap to that it would be compliant.

I have a job going right now with a similar arrangement. 3, 400 amp 3 phase fusible safety switch as mains with each feeding 3, 200 single phase subfeeds (for a total of 9 200 amp subfeeds). The ungrounded tap conductors from the 400 amp to the 200 subs are each connected directly to the 400 amp switch as this works out to 2 conductors per phase and the lugs are rated for 2 conductors. Now the neutral did need a short conductor into the wireway to tap from only because there is no way to connect 3 neutrals to the 400 amp neutral lug that is rated for only 2 conductors. In my view this is perfectly compliant and far superior to making unnecessary taps in the wireway which serve no purpose whatsoever.

While I can agree that Don's NEC proposal would clarify that this acceptable, I see the CMP's view that this is already allowed.
 
texie said:
That's absurd. ...

While I can agree that Don's NEC proposal would clarify that this acceptable, I see the CMP's view that this is already allowed.
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Absurd... but not by much.

The CMP's view is that it is already permitted... but if the inspector takes the Code verbatim (i.e. literally), you can't have a feeder tap where there is no feeder conductor. An OCPD does not qualify as a feeder conductor under the requirements of 215.2. Don's proposal should have been accepted.... but as it often happens, good proposals are often rejected only because the substantiation is insufficient in the minds of the CMP members. Perhaps he'll read this and resubmit for 2017 using the mentioned premise to enhance his substantiation.
 
Smart $ said:
Absurd... but not by much.

The CMP's view is that it is already permitted... but if the inspector takes the Code verbatim (i.e. literally), you can't have a feeder tap where there is no feeder conductor. An OCPD does not qualify as a feeder conductor under the requirements of 215.2. Don's proposal should have been accepted.... but as it often happens, good proposals are often rejected only because the substantiation is insufficient in the minds of the CMP members. Perhaps he'll read this and resubmit for 2017 using the mentioned premise to enhance his substantiation.
Click to expand...

The terminals on the OCPD are conductors.
 
iwire said:
The terminals on the OCPD are conductors.
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That's a always been my contention as well.

Regarding the OP if this "main gear" is actually the service then the taps ahead of the service disconnect would not be feeder taps and the tap rules would not apply.
 
Smart $ said:
I agree they are conductors...
Click to expand...

Great.

but they are not conductors which meet the requirements of 215.2,
Click to expand...

They do not have to meet those requirements.

and thus not feeder conductors.
Click to expand...

In my opinion article 100 says they are.

Feeder. All circuit conductors between the service equipment,
the source of a separately derived system, or other
power supply source and the final branch-circuit overcurrent
device.
Click to expand...

All is all, if you were to remove any of those components and it is no longer a circuit.
 
Do you think showing the inspector the CMP's comments on don's proposal noted in post #8 would help.

I would have allowed the 800 amp breaker "tap" to begin with, but, if I had been hesitant, that comment would have swayed me.
 
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iwire said:
Great.
They do not have to meet those requirements.
In my opinion article 100 says they are.
All is all, if you were to remove any of those components and it is no longer a circuit.
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It's not I you have to convince... it is the inspector/reviewer for OP. I am just providing a possible train of thought for interpretation, and only surmising at that...

If you remove the OCPD from the circuit in the sense the circuit is not left open, then you really have a feeder tap (tap conductors connect to the busbar, as the reviewer is requiring)... but then you have the same situation in that busbar cannot meet the requirement of 215.2. The only reference for busbar ampacity is 366.23... and I'm doubting the OP installation is in an auxiliary gutter.
 
augie47 said:
Do you think showing the inspector the CMP's comments on don's proposal noted in post #8 would help.

I would have allowed the 800 amp breaker "tap" to begin with, but, if I had been hesitant, that comment would have swayed me.
Click to expand...
I would attempt this route without hesitation, and proceed from there.
 
So, I guess as suggested earlier you can install larger conductor on the 800A ocpd then tap them with smaller conductors. That will meet the verbatim interpretation of the code.
 
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