It would seem to me that the NEC would not allow tapping the busbar in the load side of a switchboard instead of using a provided circuit breaker to land a circuit but I can't find anything in the code that would specifically prevent this. Anyone know of anything in the code that prevents this?
Tapping busbar in the load side of a switchboard allowed by the NEC?
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jaggedben
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Seems to me it is a UL issue, not an NEC issue.
Panelboards sometimes come with 'pass through' lugs. One could connect to those with no per se NEC issues. Why would a switchboard be different? I don't know if switchboard busbars would ever have holes marked 'Tap' on the load side. But I don't see any difference between load side and line side as far as the NEC is concerned.
Panelboards sometimes come with 'pass through' lugs. One could connect to those with no per se NEC issues. Why would a switchboard be different? I don't know if switchboard busbars would ever have holes marked 'Tap' on the load side. But I don't see any difference between load side and line side as far as the NEC is concerned.
That is one of the issues I see, people in the PV industry get all tap-happy on the supply side and then think, hey why can't I just add whatever I want to the load side too? Nothing matters if I have a drill, some bolts, and crimp connectors right? If that's the case why have switchboards with breakers? Just sell boxes with busbars and let everyone tap.
On top of that, I see people trying to justify it by calling a busbar tap in listed distribution equipment a feeder conductor tap in 240.21(B). That's stretching the NEC past the breaking point.
jaggedben
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I don't agree. If you tap a busbar with a lower ampacity conductor then 240.21(B) are the rules that apply to the conductors. And the NEC definition of a feeder isn't specific enough to exclude a switchboard busbar, nor does that have any bearing on the application of 240.21(B). But the manufacturer tells you how you can terminate conductors to components in a switch board, and whatever that method is, it has to be okay with the engineering and product standard. And drilling holes in busbars without any instructions certainly isn't okay, right? You need holes marked 'Tap', or unused lugs, or else probably a UL field listing that satisfies the AHJ...we know the drill (so to speak). The violation is 110.3(B), unless you can work out a way that it's not a violation.
As far as line vs. load, again, 'people' getting all 'tap happy' on listed equipment presents the same issues, line or load side, as far as I can see.
Except that a busbar in listed equipment is neither a feeder, a conductor, or a feeder conductor based on usage in the code. Since 240.21(B) applies to taps into feeder conductors it does not apply to busbar in equipment. In many places in the code, including 705.12, equipment bus and conductor are called out separately which would indicate that they are not the same components. I don't see equipment busbar in the feeder definition, just circuit conductor.
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All I have been able to find is 110.3(B) where it is a violation to perform a tap into listed equipment that is not supported by instructions from the equipment manufacturer. That should be enough to trigger an AMMR but many AHJs don't seem to feel the need to do that for whatever reason. I was wondering if I was missing something else but it seems not.
Thanks.
Thanks.
The NEC is a little vague on what a conductor and feeder are. Taken strictly at face value a fuse or CB are conductors and feeders if in the path since they conduct current. The blade of a disconnect is a conductor and a feeder. Should we tap the blade of a disconnect? I think we as engineers, designers, and electricians need to apply some common sense in interpreting the code and not expect the NEC to dot every i and cross every t for us. Is the busbar in equipment any different than the blade of a disconnect? Can we tap any of them? Let's apply some common sense here about what is safe and actually useful. But that is the basis of many a rousing disagreement over beer at a table of code nerds.
jaggedben
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I don't think that's unreasonable, but (as I was reminded here) not everyone sees it that way. And since the NEC doesn't actually define 'conductor', and since by any dictionary definition a busbar is an electrical conductor, I don't think you're going to get consensus that an 'equipment busbar' can't be a feeder or a component of a feeder. 240.21(B) also isn't one of those sections that clarifies any distinction between those two things. (Take an example I already gave: tap conductors connected to pass through lugs on a panelboard. Is there really any good reason to disallow that, and not just apply 240.21(B)?)
On the substance of your original question though, I agree with your conclusion that it really just comes down to 110.3(B).
jaggedben
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The NEC is a little vague on what a conductor and feeder are. Taken strictly at face value a fuse or CB are conductors and feeders if in the path since they conduct current. The blade of a disconnect is a conductor and a feeder. Should we tap the blade of a disconnect? I think we as engineers, designers, and electricians need to apply some common sense in interpreting the code and not expect the NEC to dot every i and cross every t for us. Is the busbar in equipment any different than the blade of a disconnect? Can we tap any of them? Let's apply some common sense here about what is safe and actually useful. But that is the basis of many a rousing disagreement over beer at a table of code nerds.
Agreed.
electrofelon
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How about this argument: panelboards (other than small resi loadcenters usually) have or can have feed thru lugs added. In that case you are using the panelboard bus as a "general purpose" conductor. That is clearly allowed, that is what feed thru lugs are for. So why cant I take a tap off it? Its just another option of sizing conductors. A while back someone tried to get a proposal in that read (something like) "taps shall be permitted to start at the lugs or terminals of equipment" but it was rejected on the basis that it was un-necessary. To me that is NEC approval.
Feed through lugs are a great way to interconnect, manufacturer approved to connect to and the panelboard is designed for it and it's not an NEC violation. Tapping a busbar somewhere unapproved is not the same, it's a violation of 110.3(B). Having feed through lugs I don't think changes the designed purpose of the busbar to a "general purpose conductor", it's just an approved connection to a busbar.
While it's hard to get in the head of the CMP members on some of these decisions it would be just as easy to think that by them saying it was unnecessary they were thinking no one would do it in the first place so why put it in the code. I have seen that in action. The CMP will reject a proposal because they do not feel someone would do the thing the proposal prevents, I've had some of mine rejected over the years based of this. Not finding something in the code is not approval to do it, it's just not a violation to do it.
DrSparks
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You mean bolting lugs to the bus bars? I do it all the time!
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electrofelon
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It seems that you are questioning two different things: One is connecting to a busbar, and the second is whether the tap rules can be applied to a "feeder bus bar" . My previous post was about the latter. Regarding the former, I think the linked article from that other thread pretty much covers it. There will no doubt be a range of opinions from inspectors on this. Most of the times it has come up for me, the inspector said as long as I didnt drill holes and used listed lugs, he was fine with it. I feel quite strongly that that is the way it should be. We make connections from a conductor to a lug all the time, and I dont see that bolting a lug onto a busbar is much different, in fact I think its harder to mess up. Besides, we bolt lugs to things in the field all the time: 320 meter sockets here dont come with lugs, GEC bus bars, grounding and bonding lugs, changing for different size and quantity of conductors......just lots of hand wringing going on when there are more imprtant things to worry about.
You mean bolting lugs to the bus bars? I do it all the time!
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I agree they are two different things. But since connecting to a busbar in listed equipment if not allowed by the manufacturer is an NEC violation I don't think someone can follow up and say that other provisions of the NEC can then be applied. The tap is a violation, how the tap conductor is sized after the violation no longer matters because we are no longer working in compliance with the NEC.
I have yet to talk to an engineer at a company that builds switchboards who agrees that tapping a busbar outside of the manufacturers' instructions is anything other than a bad idea. I'm pretty confident that they are telling the truth and have the experience to back it up. I've contacted many of them too asking if the company would approve a busbar tap in their equipment. The answer is always the same, is there a tap point marked tap? If not we don't approve. I have found a couple that will provide a kit to make an approved busbar tap, but they are few.
There are some situations where it is just unavoidable, such as connecting to the supply side of the main disconnect in existing equipment as allowed in 230.82. But in these cases at least the supply side of the disconnect is not an area that is accessed often so represents a lower risk to personnel if the tap results in a fault. The conductors on that side are already unprotected as they are directly connected to the utility distribution system where all service entrance conductors are fusible links anyway. But the load side is a different story.
electrofelon
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Note that there isnt really such thing as a "listing violation". There is 110.3(B) (and lets even ignore the debate about what exactly the instructions "included with the listing or labeling" means). So yes if I do something contrary to the instructions that is a NEC violation. Most situations we are talking about here are not specifically stated in the instructions as "do not do XYZ". In these cases it is a AHJ call based on 110.3(A). The AHJ may be ok with it, or maybe will require a UL field evaluation. One time, I had a 1200A switchboard I needed to replace, but I needed to keep the metering section. There was a bus bar joint above the CT's that conformed to NEMA standard patterns. I literally sawzalled off the buss bars on the load side of that joint, and bolted on some ilsco lugs (matching bolt pattern) and then used conductors to my new equipment. I ran the plan by the AHJ and this was a time he said "dont drill holes and use listed lugs". He was well within his right to call that based on 110.3(A). Others may have required a UL field eval. I can understand not drilling holes, but bolting on lugs on existing holes, we do that all the time: meter sockets, bussed gutters/tap boxes, brounding and bonding, etc....
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