:roll: This is a question that is a follow up to a earlier post on transformer protection (primary and secondary) Knowing that you cannot tap a transformer secondary conductor, does this mean that if you were to feed a 225A panelboard with a MCB (within 10?-0) that if that panelboard was specified or supplied with double lugs then the feeder from the set of double lugs to the adjacent panelboard would be a code violation because of no over current protection correct? For sub-feed or feed-thru lugs you would still be protected by the original panel MCB but this is not the case with double lugs. Is this line of thinking correct or am I way off base?? Thanks in advance for your thoughts.
Double-Lugs??
- Thread starter Mike01
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I would guess it may depend on where the second panel is located. The mains for a building must be grouped so if you feed the first panel and used the lugs to a second panel you would be in violation if that second panel were not next to the first one (grouped)
I hope I understood the question correctly. I was assuming the first panel is literally the first disco from the meter.
I hope I understood the question correctly. I was assuming the first panel is literally the first disco from the meter.
what about ocpd??
what about ocpd??
even if the second panel was located adjacent to the first (lets throw out 3' of cable between them) this would still be a violation correct? My reasoning is the first panel located within 10'-0" of the transformer, contains a 60A MCB (for talking purposes) lets say the panel is equipped with double lugs. The 60A MCB provides secondary protection for the feeder from the transformer secondary and the panel board, now if I connected a set of conductors to the double lug to feed another panel 3' away the conductor is not protected by the 60A MCB. Correct? so would this panel if equiped with a MCB be considered acceptable, what if it was a MLO panel then there would be not secondary overcurrent protection? Even if you had A MCB would this be considered tapping a transformer secondary conductor which is aginst the code??
what about ocpd??
even if the second panel was located adjacent to the first (lets throw out 3' of cable between them) this would still be a violation correct? My reasoning is the first panel located within 10'-0" of the transformer, contains a 60A MCB (for talking purposes) lets say the panel is equipped with double lugs. The 60A MCB provides secondary protection for the feeder from the transformer secondary and the panel board, now if I connected a set of conductors to the double lug to feed another panel 3' away the conductor is not protected by the 60A MCB. Correct? so would this panel if equiped with a MCB be considered acceptable, what if it was a MLO panel then there would be not secondary overcurrent protection? Even if you had A MCB would this be considered tapping a transformer secondary conductor which is aginst the code??
double lug
double lug
If I read correctly./.yes, still a violation...
the secondary conductors from the transf. are protected from overload by the panel circuit breraker. If you double-lug on the line side of it, the potential for overloading those conductors exists.
Someone may correct me, but I see no problem with your placing your double lugs on the transormer seconday terminals and feeding the second panel from there as long as you have proper overcurrent protection on your transformer primary.
double lug
If I read correctly./.yes, still a violation...
the secondary conductors from the transf. are protected from overload by the panel circuit breraker. If you double-lug on the line side of it, the potential for overloading those conductors exists.
Someone may correct me, but I see no problem with your placing your double lugs on the transormer seconday terminals and feeding the second panel from there as long as you have proper overcurrent protection on your transformer primary.
hardworkingstiff
Senior Member
- Location
- Wilmington, NC
augie47 said:
I quite often will take 2-3 sets of paralleled 500 CU from a MB in a panel to the PoCo transformer. They use CTs in the transformer and meter it there. Is that a violation?
hardworkingstiff
Senior Member
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- Wilmington, NC
augie47 said:
Ok, now that I've reread, if the conductors from the transformer to the panel was rated for the combined calculated loads I believe it would be safe.
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what about secondary protection
what about secondary protection
yes I believe it would be a safe installation but the code requires secondary overcurrent protection it also says you cannot tap a transformer secondary conductor, so would this be a code violation in bolth cases?
what about secondary protection
yes I believe it would be a safe installation but the code requires secondary overcurrent protection it also says you cannot tap a transformer secondary conductor, so would this be a code violation in bolth cases?
Mike01 said:yes I believe it would be a safe installation but the code requires secondary overcurrent protection it also says you cannot tap a transformer secondary conductor, so would this be a code violation in bolth cases?
Mike, you cannot extend from a panelboards main breaker line side to another panel. Article 240.21(C)(1)(2) prevents this.
(2) The tap conductors do not extend beyond the switchboard, panelboard, disconnecting means, or control devices they supply.
You can have feed through lugs on the load side of the main breaker on the buss bars.
You can also come off the transformer with multiple individual loads each having its own protection.
Rick
- Location
- Wisconsin
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- PE (Retired) - Power Systems
Remember, in 240.21 a tap is a connection to a reduced size conductor without over current protection. If the second conductor (coming out of the double lugs) is the same size as the conductor going into the lugs it is not considered a "new" tap.
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- Illinois
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- retired electrician
Jim,
Don
It is my opinion that if the first conductor is a tap, then the connection of a second conductor to the first is a second tap and not permitted by the code rules.
Don
Tap?
Tap?
This brings up a good point to a question I asked before if you do not change conductor size is it still considered a tap? If not you could run a set of 4/0 from a transformer into a wireway and splice (not tap) into two sets of 4/0 utilizing power distribution blocks like the ones manufactured by Ilsco. is this legal by code?:-?
Tap?
This brings up a good point to a question I asked before if you do not change conductor size is it still considered a tap? If not you could run a set of 4/0 from a transformer into a wireway and splice (not tap) into two sets of 4/0 utilizing power distribution blocks like the ones manufactured by Ilsco. is this legal by code?:-?
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
don_resqcapt19 said:
Don,
If the conductors going into the lug are protected under some 240.4 provision then why would the same size conductors coming out of the lug not be protected. That said, I agree that the 2005 NEC makes it clear in almost every 240.21 situation that tapped conductors (including those leaving a indoor transformer secondary) must terminate in a single protective device.
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