Temp power from MCC

[DEW202001]

This is a breaker in a MCC that is being used for temp power to a construction site. The temp cable comes into the bottom of the breaker like normal. My question is how did they power the cable with the primary conductors to the breaker cut?

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[Jraef]

It looks to me as though that bucket doesn't have a stab assembly, so someone must have run cable into the bucket through the wireway to feed it.

That is an Allen Bradley bucket, but there are no latches in the structure frame for a bucket, meaning it is probably not a section that was made to have buckets plugged in, i.e. it was originally used for something big like a VFD that would not have vertical bus bars so there is no vertical bus to stab into anyway and they just scavenged something together from leftover parts to "gitter done"..

 

[DEW202001]

Does not look very safe since it is feeding a transformer for temp power.


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[infinity]

My guess is that those taped conductors are the original load wires that were connected to the load side of the CB. They were removed and the temp conductors installed.

 

[iceworm]

This is a breaker in a MCC that is being used for temp power to a construction site. The temp cable comes into the bottom of the breaker like normal. My question is how did they power the cable with the primary conductors to the breaker cut? ...

It looks to me as though that bucket doesn't have a stab assembly, ....

Jraef -
I'm not saying you are wrong, but:
Following infinity's post:
That looks like a pretty standard AB 2100 CB bucket.
It appears to have power conductors connected to the CB line side that go out the back of the bucket - probably to stabs. If this is not true, I'm all wet. - forget the rest.

Could the taped off conductors be the old load side that originally came into the bucket from the lower right side and are now tucked up out of the way?
That catch at the bottom sure looks like the catch to allow the bucket to be pulled.

DEW - You are the only that can look and tell us.

 

[iceworm]

Does not look very safe since it is feeding a transformer for temp power. ...

Unless you have additional information about conductor sizing?

70A CB suggests a 45KVA xfm
45KVA, FLA = 54A
1.25 x 54 = 68A

70A CB is fine.

I can't tell what the conductors are, however:
310.15.B.16, 75C, #6 = 65A A little light, but likely okay for a temporary if not heavily loaded.

And if the conductors are 400.5.A.2, say Type G, #6 = 77A, that's okay.

And if 400.5.A.1, say SO #6, = 45A, not so good.

For a 30KVA, FLA = 36A X 1.25 = 45A
36 X 2.5 = 72A

So, a 70A CB is still fine.


But I still can't tell what size the conductors are.

What is it you see that is unsafe?

 

[DEW202001]

It’s a 45KW transformer.


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[iceworm]

It’s a 45KW transformer. ...

And the conductor size and cable type?

 

[DEW202001]

Correction 75KW


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[iceworm]

Correction 75KW ...

70A is pretty small for a 75KVA.
125A would be more normal.
It could be difficult to get the 75KVA to energize, 70A CB may trip on inrush. But if one tries a few times, it could hold.

The load would have to be under the 70A.
And -- we still don't know about the conductors.

Again - what are you seeing as unsafe?

 

[DEW202001]

The temp cable was hit while excavating and the breaker did not trip and it ended up trip the main breaker to the MCC shut down the waste water plant.


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[iceworm]

The temp cable was hit while excavating and the breaker did not trip and it ended up trip the main breaker to the MCC shut down the waste water plant. ...

DEW -
I see your point. Backhoes hitting live cables can definitely be unsafe. That is usually covered under 590.4.H.

[quote = DEW202001 ] Does not look very safe since it is feeding a transformer for temp power. [/quote]

I'm still at a loss as to exactly what "Does not look very safe ...".

 

[iceworm]

The temp cable was hit while excavating and the breaker did not trip and it ended up trip the main breaker to the MCC shut down the waste water plant. ...

Maybe you have a bad CB. Or, the main and the 70A overlap in the instantaneous range.

Just curious, does the MCC Main CB have a GF trip?

 

[Jraef]

Jraef -
I'm not saying you are wrong, but:
Following infinity's post:
That looks like a pretty standard AB 2100 CB bucket.
It appears to have power conductors connected to the CB line side that go out the back of the bucket - probably to stabs. If this is not true, I'm all wet. - forget the rest.

Could the taped off conductors be the old load side that originally came into the bucket from the lower right side and are now tucked up out of the way?
That catch at the bottom sure looks like the catch to allow the bucket to be pulled.

DEW - You are the only that can look and tell us.

It looked to me as though those taped conductors were coming from the top lugs on the breaker, I don't see then continuing over to the right to get to the vertical wireway. Also, normally you can see the stab assembly, that looked like just the hole / notch for it. Here's my enhanced version:

But now that we know more of the story, that doesn't make sense either because I was thinking this had already been disconnected. If it was still connected and providing power to that transformer, then something is connected to the bus.

Maybe you have a bad CB. Or, the main and the 70A overlap in the instantaneous range.

Just curious, does the MCC Main CB have a GF trip?

Yeah, that's what "coordination" is all about when doing the settings on your breakers. You want the fault to be cleared at the protective device closest to it. I'd be willing to bet the Main is over 1000A so it has GF, and the GF is set much lower than the Inst. setting of this feeder. Being an old Westinghouse breaker (pre-1995), I think that breaker had fixed magnetic trips, so likely 10x the rating, meaning the Inst. trips are factory set for 700A. Nothing wrong with that really, but if the Inst. trip or GF trip on the Main is set lower than that, the Main is going to trip first.