240.21, 408.30, 408.36

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Dale001289

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Georgia
Before I raise the red flag too high on this: Are there any circumstances under which a (42 circuit) panelboard can be installed WITHOUT a MCB, i.e. MLO? Coming from the secondary side of delta wye, 480-208/120V, 45kVA dry type transformer installed within 25 feet.

Thanks in advance.

Dale
 
Assuming you mean no disco w/OCPD between tranny and panel, right?

If so, then AFAIK nope. I do not remember a section that allows the primary protection of that tranny to directly protect a panel off the secondary.
 
jumper said:
Assuming you mean no disco w/OCPD between tranny and panel, right?

If so, then AFAIK nope. I do not remember a section that allows the primary protection of that tranny to directly protect a panel off the secondary.
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You are correct in your assumption. The primary side is protected at 125% of FLA; the secondary windings do not require protection, but the conductors do. Focusing on 408.30 and 408.36, I don't see how MLO is allowed - and this plant has it in literally in every building....
Dale
 
Dale001289 said:
You are correct in your assumption. The primary side is protected at 125% of FLA; the secondary windings do not require protection, but the conductors do. Focusing on 408.30 and 408.36, I don't see how MLO is allowed - and this plant has it in literally in every building....
Dale
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I have the same question in a very well renowned building that was installed circa 49 years ago. It has a single phase 37.5 kVA dry xfr 480 - 120/240 protected on primary by 100A. [1.25 * 37500/480 = 97.6 so 100A is good]. But guess what?? It is fed into a MLO panel. The secondary wires cannot be protected IMHO. All was at one time very well inspected. Maybe the code back then was more lax???

I have additional question also..... It has 2 wires in for the 480 which is fine and three wires out which I see as split phase 240 (L1, L2, N) but the N is not tied to the Ufer ground which is only a few feet from the panel. Can this be correct?????
 
It would only be correct, IMHO, if the secondary is intended to operate ungrounded or if the secondary neutral is connected to primary side grounded conductors to make a NON SDS.

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dionysius said:
I have the same question in a very well renowned building that was installed circa 49 years ago. It has a single phase 37.5 kVA dry xfr 480 - 120/240 protected on primary by 100A. [1.25 * 37500/480 = 97.6 so 100A is good]. But guess what?? It is fed into a MLO panel. The secondary wires cannot be protected IMHO. All was at one time very well inspected. Maybe the code back then was more lax???
Click to expand...

+40 years ago it was very common to consider the panelboard bussing as being a transformer secondary conductor for both 1-phase and 3-phase. Only relatively recently has the NEC clearly stated that they are not and thus now require a 'main' protective device. This was particularly true in areas of the country with heavy industry, which is why there are some slightly different rules for 'supervised industrial' installations.

I do not recall how we dealt with the primary protection of secondary conductors with a delta-wye winding configurations.
 
GoldDigger said:
It would only be correct, IMHO, if the secondary is intended to operate ungrounded......
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Upon further examination there are 4 sub-panels being run from OCPDs in this panel. So is this correct since the N to EGC bonding must be done only at the subpanel???? What are the reasons when you would make it non SDS by connecting primary and sec EGCs????
 
dionysius said:
Upon further examination there are 4 sub-panels being run from OCPDs in this panel. So is this correct since the N to EGC bonding must be done only at the subpanel???? What are the reasons when you would make it non SDS by connecting primary and sec EGCs????
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Saying that the neutral to EGC bond should be done only at the subpanel is exactly backwards.
There are reasons for making non-SDS, but I cannot think of any good ones when a ground electrode is so accessable.

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Dale001289 said:
You are correct in your assumption. The primary side is protected at 125% of FLA; the secondary windings do not require protection, but the conductors do. Focusing on 408.30 and 408.36, I don't see how MLO is allowed - and this plant has it in literally in every building....
Dale
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Very common around here for industrial occupancies...not sure it has ever been legal, but is very common in my area.
 
dionysius said:
I have the same question in a very well renowned building that was installed circa 49 years ago. It has a single phase 37.5 kVA dry xfr 480 - 120/240 protected on primary by 100A. [1.25 * 37500/480 = 97.6 so 100A is good]. But guess what?? It is fed into a MLO panel. The secondary wires cannot be protected IMHO......
Click to expand...

Despite the recent wording change in 240.21(C)(2)(1)(b), IMO 240.21(C)(2) doesnt require that the secondary conductors terminate on an OCPD. But, you still have 408.36 to contend with which there is no way around (unless it meets 240.21(C)(1))
 
GoldDigger said:
Saying that the neutral to EGC bond should be done only at the subpanel is exactly backwards.
There are reasons for making non-SDS, but I cannot think of any good ones when a ground electrode is so accessable.

Sent from my XT1585 using Tapatalk
Click to expand...

Re the subpanel you are correct of course.....I must have dropped out for a moment.

And yes.....this N on the secondary should be connected to the Ufer but it is not. I concur.
 
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