Conductors in Raceways

[Power2all]

Canadian Electrical Code Rule 12-904(2) states that no raceway shall contain conductors that are connected to different transformers or other different sources of voltage unless there is a separation barrier or the conductors are used to control remote devices.

Question: Can conductors connected to different transformers of same voltage be run in one raceway?

 

[DRWeig]

Based on that code passage, the answer is no -- unless there is a separation barrier.

Best to you,

Goober Dave

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[jraef]

I don't have access to the CEC, but the similar passage in the NEC is in reference to the insulation level of the conductors. Basically, if they ARE in the same raceway, all conductors must have the insulation level of the highest voltage in the raceway. So if you have 600V conductors in there, even the communications cables must be rated 600V, or behind a separate barrier.

"Will work for (the memory of) salami"

 

[waross]

Actually Dave, the answer is;
"Yes, subject to rule 12-904, subrule (2), clauses (a), (b) and (c)."
I think this is a trick question.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[Power2all]

Hi jrael, you are right in that this rule requires 120V control circuit have 600V insulation if run in the same raceway as the 600V motor leads.

I believe the intent of this rule has to do with voltage impression. It prevents having conductors of different voltages getting crossed and impressing a different voltage. That would mean I could run wiring from different source transformers as long as they are of the same voltage.... Is this your understanding?

 

[DRWeig]

jraef (and others),

I assumed all conductors had good equal insulation. The OP's question referred to conductors of the same voltage but from different transformers.

Correct me if I'm wrong, but I was thinking of potential faults involving separately-derived systems that might have an effect on whether a breaker clears them or not?

This question brought up all sorts of thoughts in my scrambled brain. I have never investigated it because it has never come up for me. I hope my questions are taken as expanding on the OP's post. I don't mean to hijack the thread.

What happens when there is a L-L fault between a phase from one system and a phase from another system?

What about if I accidentally parallel two three-phase transformers on one phase only when they share a common ground? I might do that if I were an electrician opening a junction box and seeing six phases coming in one pipe.

What if the two transformers' grounds are a significant distance apart, so there might be circulating current issues?

Best to you,

Goober Dave

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[waross]

Rule 12-904 (2),
(a) are separated by the metal armour or metal sheath of cable assemblies of the types listed in Table 19;
(b) are separated by a barrier of sheet steel not less that 1.34 mm (No. 16 MSG) thick or a flameretardant
non-metallic insulating material not less than 1.5 mm in thickness; or
(c) are used for the supply and/or control of remote devices, are insulated for at least the same voltage
as that of the circuit having the highest voltage, and none of the conductors of the circuits of lower
voltages is directly connected to a lighting branch circuit.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[rcw retired EE]

A Canadian inspector told me the rule was to prevent inadvertent interconnection of two power sources. With two white neutral wires in the same raceway, a 120V circuit from Transformer Tx1 could be connected to the neutral from Transformer Tx2's neutral. The circuit might work, but the load current would flow in both transformers' neutral bonding jumpers and in the ground(s) between the two.

 

[DRWeig]

Thanks waross and rcwilson.

Best to you,

Goober Dave

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[waross]

I see this rule applied most often when control conductors are run in the same raceway as power conductors. Most times the 600V or 480V power circuit does not have a neutral.
But I don't see everything and there are always exceptions..

Bill
--------------------
"Why not the best?"
Jimmy Carter