12 volt alarm field wiring grounded conductor color

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andy32821

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Orlando, Fl
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A 12 volt 5 amp alarm power supply (not class 2) feeds misc devices throughout a commercial facility via a single pair belden cable with one black and one white conductor. The belden cable is installed in EMT.

The negative side of the 12 volt 5 amp power supply output is intentionally grounded.

Does the NEC require the to be negative (grounded conductor) to be the white conductor?

The electronic techs are hung up on the black wire being negative, I just need to sign off that the system meets NEC.

Thanks,
Andy
 
S'mise

S'mise

Senior Member
Location
Michigan
andy32821 said:
A 12 volt 5 amp alarm power supply (not class 2) feeds misc devices throughout a commercial facility via a single pair belden cable with one black and one white conductor. The belden cable is installed in EMT.

The negative side of the 12 volt 5 amp power supply output is intentionally grounded.

Does the NEC require the to be negative (grounded conductor) to be the white conductor?

The electronic techs are hung up on the black wire being negative, I just need to sign off that the system meets NEC.

Thanks,
Andy
Click to expand...

Dont think it matters, I believe its a class 2 look at table 11(B) and read art 725
 
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nhfire77

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It's not CL2? Are you sure?

Intentionally grounding a CL2 power supply is improper. The system is intentionally floated from ground. You should check the labeling and installation instructions of the power supply. It is possible its some unusual unit.

Color coding of CL2 does not have the restrictions normally placed on grey, white and green conductors
 
S'mise

S'mise

Senior Member
Location
Michigan
nhfire77 said:
It's not CL2? Are you sure?

Intentionally grounding a CL2 power supply is improper. The system is intentionally floated from ground. You should check the labeling and installation instructions of the power supply. It is possible its some unusual unit.

Color coding of CL2 does not have the restrictions normally placed on grey, white and green conductors
Click to expand...

The PS may not be marked but 12v 5a is class 2.

It does sound improper to ground it. Can you explain what its wrong with doing so, and what code it may violate?
 
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nhfire77

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S'mise said:
The PS may not be marked but 12v 5a is class 2.

It does sound improper to ground it. Can you explain what its wrong with doing so, and what code it may violate?
Click to expand...



You are probably violating the manufacturers instructions, violating the UL listing.

It intentionally uses the conduit, and the enclosure, to carry current, kinda unsafe, and I'm sure if it wasn't 5am I could find something prohibiting that in this example.
 
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andy32821

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Location
Orlando, Fl
Occupation
Automation
update

update

Let's assume these are not class 2 transformers and the total available amperage is 30 amps.

The grounding of the power supply is like the grounding of one leg of a power transformer.
Current does not flow through condiut unless there is a ground fault.

So the question I am trying to ask is:

Does the NEC require a grounded conductor of a 12 volt (non class 2) to be white in the same way that the NEC requires a grounded conductor of a 120 volt system to be white?

Thanks,
Andy
 
don_resqcapt19

don_resqcapt19

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andy32821 said:
...
Does the NEC require a grounded conductor of a 12 volt (non class 2) to be white in the same way that the NEC requires a grounded conductor of a 120 volt system to be white?

Thanks,
Andy
Click to expand...
In my opinion, if the circuit is not covered by the rules in Chapters 5-8, then it must comply with the identification rules found in Article 200 if it is a grounded conductor.
 
don_resqcapt19

don_resqcapt19

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Location
Illinois
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retired electrician
nhfire77 said:
You are probably violating the manufacturers instructions, violating the UL listing.

It intentionally uses the conduit, and the enclosure, to carry current, kinda unsafe, and I'm sure if it wasn't 5am I could find something prohibiting that in this example.
Click to expand...
Grounding a conductor of a system does not use the conduit and the enclosure to carry current under normal conditions. There may be current flowing on those items in the event of a ground fault, but why would that be an issue for a low voltage system when it is not for power systems?
 
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nhfire77

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don_resqcapt19 said:
Grounding a conductor of a system does not use the conduit and the enclosure to carry current under normal conditions. There may be current flowing on those items in the event of a ground fault, but why would that be an issue for a low voltage system when it is not for power systems?
Click to expand...



I inferred he was using the EMT on the negative side of the load, so the load would be using the EMT as its normal return path, not just in a fault condition.

I guess I need to ask, is it just attached to ground just at the power supply, or at the devices as well, I'm picturing a bond to EMT at each device. But, that wasn't stated, I may have got ahead of myself.
 
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S'mise

S'mise

Senior Member
Location
Michigan
nhfire77 said:
I inferred he was using the EMT on the negative side of the load, so the load would be using the EMT as its normal return path, not just in a fault condition.

I guess I need to ask, is it just attached to ground just at the power supply, or at the devices as well, I'm picturing a bond to EMT at each device. But, that wasn't stated, I may have got ahead of myself.
Click to expand...

A bond to EMT at each device would cause loops (paralell paths) IMO, thats the worst way to wire it. You would introduce noise on the DC.

All arguments could be settled if the OP posted the PS and alarm panel name and model.
 
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