Transformer Secondary Conductors

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Mike01

Mike01

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Can transformer secondary conductors be tapped? if there is no secondary overcurrent protection?? Can you provide a single set of conductors (not to exceed 10'-0") to a wireway and then tap that conductor to a smaller conductor to feed more than one mcb panelboard, or do I need to run a indivigual set of feeders from each panelboard directly connected to the transformer secondary??:confused:
 
Mike01 said:
Can transformer secondary conductors be tapped? if there is no secondary overcurrent protection?? Can you provide a single set of conductors (not to exceed 10'-0") to a wireway and then tap that conductor to a smaller conductor to feed more than one mcb panelboard, or do I need to run a indivigual set of feeders from each panelboard directly connected to the transformer secondary??:confused:
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Isn't there a rule about the OCPD size on taps? If there is no OCPD, how would you ever meet that requirement?
 
Mike,
You can't tap a tap and that is what you would be doing.
240.21 Location in Circuit
Overcurrent protection shall be provided in each ungrounded circuit conductor and shall be located at the point where the conductors receive their supply except as specified in 240.21(A) through (G). No conductor supplied under the provisions of 240.21(A) through (G) shall supply another conductor under those provisions, except through an overcurrent protective device meeting the requirements of 240.4.
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Don
 
:D Thanks, that was my thought to, where is this stated in the code I could not locate it I will continue to look it probally says that just in a different way. The argument was that these are not taps they are transformer secondary conductors....
 
I think it is worth pointing out that while you can not tap the conductors you can run more than one set of conductors off the transformer itself to other over current protective devices.
 
True

True

This was the discussion we use this all the time utilizing multiple transformer taps to feed seprate panels (10' tap rule) but some people in our office were feeding a wireway with a single set of conductors then tapping that conductor to feed more than one panel and this woul be a code violation. Is it still considered a tap if the conductors do not change size? I also noticed that in the NEC it requires the cable to be rated for the ocpd it terminates in. The only other method I have seen is someone will put an ocpd on the secondary feed that into a wireway and then tap that conductor. Thanks for the code reference I probally should have read the whole thing befor responding I apoligize for that just jumped the gun.
 
Mike,
Is it still considered a tap if the conductors do not change size?
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Yes, even if you do not change sizes it is still a tap as the conductor is not protected at its ampacity at its supply point.
Don
 
Ocpd

Ocpd

When you provide multiple sets of feeders to multiple panels from the secondary of a transformer (10' rule) the conductors are then being protected by the MCB in the panel correct? this is where note#2 on the xfmr chart comes into play correct? these MCB's act as secondary overcurrent protection therefore note#2 would apply. Also not seeing too many xfmr's in my time (open at least) how do you know how many connections you can get per phase with what size cable?? I would assume you have to verify this with the manufacturer or will the customize this portion of the xfmr to accept what is indicated on the drawings? Just a thought because a xfmr is only so big and if you have 3 - 4 conduits you would have to makes sure you have the space to put the conduits not to metion the lugs on the xfmr.
 
hmm..just thinking

hmm..just thinking

No conductor supplied under the provisions of 240.21(A) through (G) shall supply another conductor under those provisions, except through an overcurrent protective device meeting the requirements of 240.4.
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Does this mean as long as I provide overcurrent protection I can do this??? or is it as Don metioned that because the "tap as the conductor is not protected at its ampacity at its supply point" because where the tap occurs you would be supplying another conductor. supplying being the key word where there is no overcurrent protection..tricky topic..

The main reason I ask is because I am currently working on a facility a renovation where the building is reletative new less than 5 years old, looking at the one-line and riser diagrams in some situtations it indicates a transformer with secondary conductors into a wireway (say 500's) then three panels hanging off the wireway fed with 250's my interperatation would be code violation you are tapping a tap, in another spot there is a 75kva xfmr with 1 set of 4/0 secondary conductors into a wireway, two panels hanging from the wireway fed with 4/0 conductors the conductors did not change size but the secondary conductors were tapped to make this connection..still a violation because where the second set of 4/0 get their supply they are not protected. it sound like someone was trying to apply the tap rule twice once to secondary conductors and then again providing protection in the form of a MCB is that code compliant I would not think so, but some engineers in the office agree and some do not I personally think this is a code violation, but this buiding is up and operating and like I said is less tha 5 years old. I am intrested to hear some more of your opinions.
 
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In my opinion those are code violations. If you have a conductor that does not have overcurrent protection at its line end it is a tap and any conductor connected to that, no matter what size, is a tap of a tap and is not permitted. Just because it was designed, installed and inspected does not always mean it is not a code violation.
Don
 
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