Bare Copper Bus Bar as Open Wiring Method

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Steve Merrick

Member
Location
Anchorage, AK
Can bare copper bus bar be used as an “open wiring on insulators” wiring method in accordance with NEC 398?

Our consultants have designed a battery room where the POS and NEG terminals of a 250 VDC stationary battery land on individual sections of wall-mounted copper bus bar located about 6 feet apart on insulated standoffs, before continuing on to the DC breaker panel. The bus bars and terminal lugs are protected by acrylic covers and otherwise meets the requirements of Article 398. Additionally, our application looks identical to the last two sentences of 300.37, however that wiring method appears to only be allowed above 1000 volts.

I think we're OK under Article 398, but one of our contracted electrical inspectors has given us an unsatisfactory finding because the bus bar is not UL listed for the application (the bar is listed for grounding applications only). To my knowledge, there is no UL listing for bare copper bus bars used as a power circuit conductor; just as in nob-and-tube wiring methods, the bare circuit conductors are not UL listed but are still approved wiring methods.

Your guidance and opinions are requested.

Thanks!
 

luckylerado

Senior Member
The bar must have an ampacity no? Does that not indicate power rated?

During my first year or two in the field I was on a telco route installing battery rooms in the way you describe all over the south and Midwest. Nothing recent though.:(

Is this cheaper than cabling it?
 

Steve Merrick

Member
Location
Anchorage, AK
The bar must have an ampacity no? Does that not indicate power rated?

During my first year or two in the field I was on a telco route installing battery rooms in the way you describe all over the south and Midwest. Nothing recent though.:(

Is this cheaper than cabling it?

Yes, the bus bar was supplied by Burndy and carried an ampacity rating. Burndy states in its bus bar literature: "UL listed for grounding. Can be used for 'power' applications as well."
 

iwire

Moderator
Staff member
Location
Massachusetts
Can bare copper bus bar be used as an “open wiring on insulators” wiring method in accordance with NEC 398?

No.

Open wiring on insulators are not bare, they are insulated.


398.2 Definition.

Open Wiring on Insulators. An exposed wiring method using cleats, knobs, tubes, and flexible tubing for the protection and support of single insulated conductors run in or on buildings.

In other words it's talking about knob and tube.
 

Carultch

Senior Member
Location
Massachusetts
Can bare copper bus bar be used as an “open wiring on insulators” wiring method in accordance with NEC 398?


I do not think there is any application that is governed by the NEC, where exposed bare copper anything can be used as a current-carrying conductor, outside of a piece of manufactured product.
 

Steve Merrick

Member
Location
Anchorage, AK
Yes, I also see it as similar to an open knob and tube installation. It looks strange to me, but I can't find anything to prohibit it under the Code. ...And honestly, the two terminal bars are much less exposed than the 240 open battery posts and intercell connections on the 250 VDC battery.

I asked the design engineer why the bus bar to cable setup is not installed in a box. He told me a box is not required under 300.16(B). The conduit is fitted with an insulated bushing as described in 300.16(B). While unusual, this seems permissable in this instance.

What are we missing?
 

iwire

Moderator
Staff member
Location
Massachusetts
Yes, I also see it as similar to an open knob and tube installation. It looks strange to me, but I can't find anything to prohibit it under the Code. ...

Are you sure the NEC applies to this installation?

But exposed copper bus bars are not a recognized wiring method see 110.8

Than there are the OSHA rules prohibiting employees from being exposed to live parts.
 

Steve Merrick

Member
Location
Anchorage, AK
Are you sure the NEC applies to this installation?

But exposed copper bus bars are not a recognized wiring method see 110.8

Than there are the OSHA rules prohibiting employees from being exposed to live parts.

I don't know why open busbar would not be allowed under 110.8. Copper and aluminum bars are an approved wiring method under 110.36 Circuit Conductors ("Circuit condustors shall be permitted to be installed... as bare wire, cable and busbars"), 300.37 Aboveground Wiring Methods ("...bare busbars shall also be permitted"); 310.15(A)(1) Tables or Engineering Supervision (ampacity of busbar determined by engineers); Table 310.15(B)(2)(a) IN#2 (ampacity adjustment of bare copper and aluminum bars); Table 310.15(B)(21) (bare conductors in free air); and 366.23(A) (ampacity of bare copper and aluminum bars in auxiliary gutters). Am I missing something?

It is should not be an OSHA or NFPA 70E issue, as terminal bar is not "Exposed," which is defined as "capable if being inadvertently contacted by a person," and not "suitably guarded, isolated or insulated." The terminal bus bars are protected by sturdy Lexan covers and are both guarded and isolated.
 

abrace

Member
Location
New Hampshire
Occupation
Telecommunications Engineering
Code compliant or not, this is done all over the Telco industry as you mention in negative 48V systems. Acrylic plastic shields and covers are usually put over exposed bus bars, but you could still touch the bar if you wanted to. Only done in locked rooms with limited access only by qualified persons :thumbsup:.
 

iwire

Moderator
Staff member
Location
Massachusetts
Code compliant or not, this is done all over the Telco industry as you mention in negative 48V systems.

Of course it is, but those are not under the NEC or the same OSHA rules as other employers.

That is why I asked if this installation was under the NEC or not.
 

iwire

Moderator
Staff member
Location
Massachusetts
I don't know why open busbar would not be allowed under 110.8. Copper and aluminum bars are an approved wiring method under 110.36 Circuit Conductors

110.36 is for over 600 volts

("Circuit condustors shall be permitted to be installed... as bare wire, cable and busbars"), 300.37 Aboveground Wiring Methods ("...bare busbars shall also be permitted");

300.37 is also for above 600 volts

It is should not be an OSHA or NFPA 70E issue, as terminal bar is not "Exposed," which is defined as "capable if being inadvertently contacted by a person," and not "suitably guarded, isolated or insulated." The terminal bus bars are protected by sturdy Lexan covers and are both guarded and isolated.

I would not want to have the argument with OSHA.
 

scrypps

Member
Location
United States
I do not think there is any application that is governed by the NEC, where exposed bare copper anything can be used as a current-carrying conductor, outside of a piece of manufactured product.

They do it all the time in phone buildings. Very large bare bussing everywhere. The trick is that it is only 48v.
 

iwire

Moderator
Staff member
Location
Massachusetts
They do it all the time in phone buildings. Very large bare bussing everywhere. The trick is that it is only 48v.

Being 48 volts is not the trick, the trick is that those installations are not covered at all by the NEC. The NEC does not apply to those parts of a phone company


90.2(B) Not Covered. This Code does not cover the following

(4)Installations of communications equipment under the exclusive control of communications utilities located outdoors or in building spaces used exclusively for such installations
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
Being 48 volts is not the trick, the trick is that those installations are not covered at all by the NEC. The NEC does not apply to those parts of a phone company
But OSHA does, they just use a different basic industry safety code for the electrical component on which their OSHA plan is based.
 

GoldDigger

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Location
Placerville, CA, USA
Occupation
Retired PV System Designer
Could have sworn I mentioned that some posts ago. :cool:

You did, but I think you are wrong in saying (or implying) that the OSHA rules they operate under are different. The policies and standards developed to comply with OSHA may be different, but the OSHA rules themselves are not, AFAIK.
 

iwire

Moderator
Staff member
Location
Massachusetts
You did, but I think you are wrong in saying (or implying) that the OSHA rules they operate under are different. The policies and standards developed to comply with OSHA may be different, but the OSHA rules themselves are not, AFAIK.

The OSHA rules that apply to electricians are different rules than apply to power line workers. I am not sure where communications workers fit in
 

Steve Merrick

Member
Location
Anchorage, AK
I must be dense, but I am still not getting why bus bars are not allowed as a wiring method. First, a little more background: this is in a remote location up on the Arctic tundra with no electric utility service - rather, we are our own utility, installing generators and distribution equipment as needed. The battery and its small charger are the only sources of power available for a number of large remote petroleum valve and metering and communication system up on the North Slope in Alaska. As such, the battery terminal plate can be considered part of the service entrance conductor under Article 230.2(A). Article 230.43(1) lists "open wiring on insulators" as an approved wiring method for service entrance conductors operating at 1000V and below, and is also an approved wiring method under 398.10. The main question is whether bus bars can be used as a wiring method in place of stranded cable in the open wiring method.

Bus bars are used everywhere in industry, in panel boards, switchboards, MCCs, transformers, stationary battery intercell connectors and terminal plates, etc. None of them are UL listed. UL does not have a standard for bare copper bus bar used as power conductors. For example, UL891 for Deadfront Switchboards allows silver, copper or aluminum busbars, and goes into great detail on mounting, bracing, ampacity and other bus bar design requirements, but nowhere does it require the bus bars to be UL listed/labeled. Other components in the panels must be listed and labeled, including breakers, relays, indicators, connectors, etc. This is consistent with UL listing/labeling requirements for bare copper wire - there are none.

While I believe the NEC allows bus bar as a wiring method under Article 398 for industrial establishments, I freely admit that I could be wrong - that's why I am asking for your sage wisdom here. However, if I am wrong, then literally thousands of stationary battery applications in non-utility establishments like ours are also out of compliance. This would include everyone with a large UPS where the cells in the battery string are connected with terminal bars (not wires) and the charger and battery cables land on a common terminal plate (bus bar) for each main terminal. It would aso include backup generator starter battery strings and many more applications. If bus bars on batteries are indeed not an approved wiring method, then it should be considered by the Code Board for a future revision.

Sorry for writing War and Peace...
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
While I believe the NEC allows bus bar as a wiring method under Article 398 for industrial establishments, I freely admit that I could be wrong - that's why I am asking for your sage wisdom here. However, if I am wrong, then literally thousands of stationary battery applications in non-utility establishments like ours are also out of compliance. This would include everyone with a large UPS where the cells in the battery string are connected with terminal bars (not wires) and the charger and battery cables land on a common terminal plate (bus bar) for each main terminal.

1. If the battery bank nominal voltage is 48VDC or lower, the NEC does not restrict the wiring methods.
2. If the UPS is considered a single piece of equipment with only factory wiring on the batteries rather than field wiring, then NEC would not apply even with higher battery voltages.
3. If the wiring is inside a cabinet with restricted access, the NEC will not care as much about the wiring methods.
 
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