Safety of Tapping Service Conductor

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bcm

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Hi friends!

I have a bit of a quandry with an inspector and an electrician about tapping service conductors and "safety".

There are existing 750 MCM service conductors in a trough. The design was to tap those 750 MCM conductors to add a new service point (meter/disconnect) for some cellular cabinets. The 750 MCMs are also tapped inside the trough to feed some other meters. At least one of the meters is fed by a set of 250 MCM. The electrician, instead of tapping the 750 MCM moved down the trough and tapped the 250 MCM before one of the meters and pulled #3/0s for the new meter. He claimed it was "safer" to do this than to tap the 750 MCM like everybody else did.

The local inspector isn't happy with what was done, but I haven't been able to get him to respond to me about why this is an issue.
I have my own instincts that say the electrician should be tapping somebody else's conductors for our client's meter, but I'm at a loss beyond that. So far, I haven't found anything helpful in the NE

Do you folks have any idea (outside of "it doesn't match the drawings") why the electrician would say tapping the 250MCMs are "safer" and why the inspector would be against doing this?

Thanks so much!
 
You cannot tap a tap.

240.21(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). The provisions of
240.4(B) shall not be permitted for tap conductors.
 
jumper said:
You cannot tap a tap.

240.21(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). The provisions of
240.4(B) shall not be permitted for tap conductors.
Click to expand...

If they are service conductors that does not apply.

If they are service conductors with multiple service disconnects all that matters is the calculated load.

230.90(A) Exception 3.
 
You cannot tap a tap.

240.21(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). The provisions of
240.4(B) shall not be permitted for tap conductors.

Can't tap a tap... short and sweet. That was my thinking too, but the wording of 241.21(B) confused me a bit since it said "feeder taps" rather than taps in general or "service taps".

Is there any reason that tapping a tap (despite being against code) would be "safer"?

My only thought is that the electrician chose to tap AFTER the disconnect for the 750 MCMs rather than before it like the design specified, but it still doesn't explain why he didn't just tap the 750 MCMs. I can't figure why he chose to tap the 250 MCMs already serving as a tap.

What a conundrum! Thanks!
 
bcm said:
You cannot tap a tap.

240.21(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). The provisions of
240.4(B) shall not be permitted for tap conductors.

Can't tap a tap... short and sweet. That was my thinking too, but the wording of 241.21(B) confused me a bit since it said "feeder taps" rather than taps in general or "service taps".

Is there any reason that tapping a tap (despite being against code) would be "safer"?

My only thought is that the electrician chose to tap AFTER the disconnect for the 750 MCMs rather than before it like the design specified, but it still doesn't explain why he didn't just tap the 750 MCMs. I can't figure why he chose to tap the 250 MCMs already serving as a tap.

What a conundrum! Thanks!
Click to expand...

See Bob's reply, I missed the boat........it happens.
 
iwire said:
If they are service conductors that does not apply.

If they are service conductors with multiple service disconnects all that matters is the calculated load.

230.90(A) Exception 3.
Click to expand...
_________________________________________________________________
I'm trying to get my field guy to verify that the existing 1200A switch is a service entrace rated disconnect switch or not. I'm thinking if he finds the 1200A switch between the transformer and the trough (that has meters tapped from it) is grounded, that makes it the SER. Is there more about an SER that I'm missing? NEC 230's definition sounds almost too simple.
 
Overlooking the "tapping a tap" for the moment. What does the 250 kcmil feed (beyond the meter) ?
It would seem likely that the 250 kcmil, a 255 amp conductor, would be overloaded by add the load of the 3/0 (200 amp) tap.
Load calculations might show a violation.
 
augie47 said:
Overlooking the "tapping a tap" for the moment. What does the 250 kcmil feed (beyond the meter) ?
It would seem likely that the 250 kcmil, a 255 amp conductor, would be overloaded by add the load of the 3/0 (200 amp) tap.
Load calculations might show a violation.
Click to expand...
______________________________________
I don't know what the 250 MCM is feeding, but the point about overload is also a very good one.
 
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