Does the NEC permit tapping a bus?

Status
Not open for further replies.
M

mollydodger

Member
Is it permitted to tap a bus (service conductor) inside a 1200A 3phase service enclosure to add conductors, exit the enclosure and run to another enclosure twenty feet away? I can't see where this is allowed. I believe that NEC violations exist such as: No OCPD at the source of supply and UL listing problems because the equipment is being field modified (drilling the bus) to allow the addition of the conductors. If this is permitted for one set of conductors then would it be Ok to do it with three, or seven, or ten??? Where would it stop??? I believe that it is not permitted by code. all thoughts welcome and if you have a code reference that permits such a practice please provide it. Mr. Holt....comments?????
 
mollydodger said:
Is it permitted to tap a bus (service conductor) inside a 1200A 3phase service enclosure to add conductors, exit the enclosure and run to another enclosure twenty feet away? I can't see where this is allowed. I believe that NEC violations exist such as: No OCPD at the source of supply and UL listing problems because the equipment is being field modified (drilling the bus) to allow the addition of the conductors. If this is permitted for one set of conductors then would it be Ok to do it with three, or seven, or ten??? Where would it stop??? I believe that it is not permitted by code. all thoughts welcome and if you have a code reference that permits such a practice please provide it. Mr. Holt....comments?????
Click to expand...

This is not really an NEC issue. It depends on if it is acceptable to the manufacturer and the AHJ. If the manufacturer says no then you need to look at 110.3(B).
 
Also even if the manufacturer says it is ok to tap the bus, I would not consider 20' away as "grouped" and 230.72(A) requires the service disconnects to be grouped.
 
mollydodger said:
Is it permitted to tap a bus (service conductor) inside a 1200A 3phase service enclosure to add conductors, exit the enclosure and run to another enclosure twenty feet away? I can't see where this is allowed. I believe that NEC violations exist such as: No OCPD at the source of supply and UL listing problems because the equipment is being field modified (drilling the bus) to allow the addition of the conductors. If this is permitted for one set of conductors then would it be Ok to do it with three, or seven, or ten??? Where would it stop??? I believe that it is not permitted by code. all thoughts welcome and if you have a code reference that permits such a practice please provide it. Mr. Holt....comments?????
Click to expand...


Service conductors do not have OCPDs at their supply.


Aside from that, as Don has mentioned, there may be a grouping issue.
Also, when someone wants to tap a bus, I ask them to provide me with a letter from the manufacturer if it will be permitted as per their requirements. Also, if they do permit it, they will generally specify locations on the bus where it is permitted.
I would say it is a 50/50 chance they will, based on the past responses I have had experience with.
 
Tapping a bus inside service gear

Tapping a bus inside service gear

Pierre C Belarge said:
Service conductors do not have OCPDs at their supply.


Aside from that, as Don has mentioned, there may be a grouping issue.
Also, when someone wants to tap a bus, I ask them to provide me with a letter from the manufacturer if it will be permitted as per their requirements. Also, if they do permit it, they will generally specify locations on the bus where it is permitted.
I would say it is a 50/50 chance they will, based on the past responses I have had experience with.
Click to expand...

When I mentioned no OCPD I was referring to the fact that NEC requires overcurrent protection at the point conductors receive their supply. These do not have any. They are bolted to the service equipment bus, exit the service enclosure and extend a distance to another enclosure where they are terminated. Many folks seem to believe the bus in a service enclosure is a feeder. It is not. I do not see where the NEC mentions or permits tapping a bus. There are rules for tapping feeders, transformer secondaries, branch circuits and BUSWAYS but not service bus. Each method permitted has very specific limitations and requirements that must be met. If it did then why would we ever require any OCPDs at the souce for the FEEDERS that typically receive their supply from the exact same bus??? If you can tap the bus once without OCPD and exit the service enclosure, why not every time?? I also question any manufactuer that would agree to such a scenario rather than recommend an upgrade of the equipment which has obviously reached its maximum physical design capacity. As a maker of equipment I would certainly rather sell a new and profitable piece of gear rather than field modify some old gear that probably should be replaced anyway.
 
It is my opinion that the bus is a service entrance conductor and the code permits service entrance conductors to be tapped. The fact that it is a bus does make it a special case requiring the approval of the manufacturer. 230.46
 
don_resqcapt19 said:
It is my opinion that the bus is a service entrance conductor and the code permits service entrance conductors to be tapped. The fact that it is a bus does make it a special case requiring the approval of the manufacturer. 230.46
Click to expand...

I agree with Don, and you can tap it several times. If you have a pull can in the middle and two sets of meters on each side that is all bussed together, it's the same as tapping it and putting another meter section next to one of those existing two.

You don't have to have an OCPD where the feeders recieve their supply as long as you meet the tap rules, which sometimes make it harder than putting in a OCPD.
 
John,
I don't think that the tap rules apply to service taps. The length of the taps is limited by the requirement that the service disconnects and OCPDs be grouped. The OCPD at the load end of the tap would have to be rated at or below the ampacity of the tap.
 
don_resqcapt19 said:
John,
I don't think that the tap rules apply to service taps. The length of the taps is limited by the requirement that the service disconnects and OCPDs be grouped. The OCPD at the load end of the tap would have to be rated at or below the ampacity of the tap.
Click to expand...

Well I apply them to services. I have a lot of companies here that are leasing out space to telecom groups, and if you want to tap a 100 amp meter off of 3000 amp switch gear then you are going to meet the rules.

I do agree with the second part.
 
John,
... if you want to tap a 100 amp meter off of 3000 amp switch gear then you are going to meet the rules.
Click to expand...
What rules? The tap rules in Article 240 do not apply to service conductors. The rule in 230.90(A) covers the overload protection of the service conductor tap and the disconnect "grouping" rule covers the length. The only thing that you don't have in Article 230 is the 1/10 or 1/3 ampacity rules that we have in the 10' and 25' tap rules.
 
don_resqcapt19 said:
What rules? ... The only thing that you don't have in Article 230 is the 1/10 or 1/3 ampacity rules that we have in the 10' and 25' tap rules.
Click to expand...

The length of unprotected service conductors inside of buildings is subject only to local codes and the AHJ. The NEC does not specify a maximum length.
 
don_resqcapt19 said:
John,

What rules? The tap rules in Article 240 do not apply to service conductors. The rule in 230.90(A) covers the overload protection of the service conductor tap and the disconnect "grouping" rule covers the length. The only thing that you don't have in Article 230 is the 1/10 or 1/3 ampacity rules that we have in the 10' and 25' tap rules.
Click to expand...

If you tap ahead of the main you don't have any overload protection. I don't see any thing is 230 that covers length.

Most engineers will spec the distance on the plans, I'm assuming because they are applying the tap rules.
 
cowboyjwc said:
If you tap ahead of the main you don't have any overload protection. I don't see any thing is 230 that covers length.
Click to expand...
The length is indirectly covered by the disconnect "grouping" rule. If you are tapping the service bus, you are adding another service disconnect and assuming that they are both on the same meter, the service disconnects have to be grouped. If you are feeding a second set of service entrance conductors for another occupancy there is no grouping rule and no rule limiting the length, however the conductors in this case can't be run inside the building.
 
don_resqcapt19 said:
The length is indirectly covered by the disconnect "grouping" rule. If you are tapping the service bus, you are adding another service disconnect and assuming that they are both on the same meter, the service disconnects have to be grouped. If you are feeding a second set of service entrance conductors for another occupancy there is no grouping rule and no rule limiting the length, however the conductors in this case can't be run inside the building.
Click to expand...

Ok, that I will agree with.
 
Status
Not open for further replies.
Top