24vdc run with 120 vac

[jcraft]

I was wondering if it would be okay to run some 24Vdc power wiring in the same conduit as 120Vac wires.

 

[dV8r]

Its OK with me.
Others, like your insurance carrier, may disagree though.

 

[dpc]

It's allowed by NEC, as long as the 24 V DC wiring is insulated for at least 120 V, or the highest voltage you have present in the conduit.

 

[TWControls]

I think the big question is what is on the other end of the 24VDC wiring? Is it susceptible to noise?

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TW Controls -

http://www.twcontrols.com

 

[itsmoked]

Wire run thru conduit is often not twisted and so is very likely to have cross coupling. If it's a bunch of light bulbs who cares? If it is control signals.. Everyone will care.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[dbaird]

If it pertains to your installation, review the following recommendations per Allen Bradley Publication 1770-4.1 ("Industrial Automation Wiring and Grounding Guidelines").

http://download.yousendit.com/7A4639BF673D255C

David Baird

Sr Controls Designer
EET degree.
Journeyman Electrician.

 

[controlsdude]

your just asking for trouble. Any noise on the 120VAC will show on 24VDC. BAD things will happen, trust me, it will.

 

[HCBFlash]

just my 2 cents,

You say 24VDC POWER, but don't tell us much about the 120V. POWER may well not be particularly suceptible to noise, and the 120VAC won't notice the 24VDC. I've done it, and don't recall any issues coming up.

Insulation rating, as dpc mentions, is a basic requirement.

Please let us all know how this works out for you! and don't forget faq731-376

 

[Lancie1]

JCraft,
Please use SHIELDED 300-volt-rated cable for your 24 VDC power. Then you will have no problems when you run the shielded cable with the 120 votl wires. Shielded cable gives about the same level of noise protection as runnning the wires in a separate conduit. What's the big deal?

 

[ScottyUK]

Shielding is only effective at reducing capacitively coupled interference. If it is inductively coupled then the shield might as well not be there for all the effect it will have. A cable layed with a fairly tight twist will have some resistance to inductive coupling.

Whether the parallel run of 120V and 24V is a factor in this specific installation depends on the nature of the load on the 120V circuit and the load on the 24V circuit, and the luck of the draw how the cables lay in the conduit. In the latter case the answer is usually 'in the most inopportune manner imaginable'. At least, that's how it is in my world.

We don't use a lot of conduit in the UK so the chances are I'd be using two separate SWA cables if possible - I have gotten away with 120V sharing a multicore with 24V in a breakdown situation but have made a proiper job of it later.


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