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I have 110VDC supplied by a controller to power a actuator/motor located in a hazardous C1D1 environment. I wish to install a disconnect downstream of the controller in the hazardous location so the technicians may cut power to the actuator during maintenance. Though it is a 110VDC system, will a 30A 600VAC nonfused disconnect work? The disconnect enclosure will be explosion proof, as well as the conduit and actuator itself, but I'm not sure if DC arcing within the disconnect would be a problem. The UL rating on the disconnect says VAC only. Motor will typically sit idle, and will only be used in emergency situations.

Motor data: Rated Load Amps - 6.3 Nominal Load Amps - 4.9 Nominal Motor H.P. - .45

ThatGuyEE
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2 Answers2

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Though it is a 110VDC system, will a 30A 600VAC non-fused disconnect work?

When a contactor opens that is carrying AC current, the arc extinguishes as the AC passes through zero; this doesn't happen with DC so you need to find a contactor that is appropriately rated for 110 volts DC.

I'm not sure if DC arcing within the disconnect would be a problem.

Maybe you are more sure now.

Andy aka
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No, you can't just presume that. You need to actually read the nameplate and instructions and see what the disconnect is rated for.

DC, particularly in voltages above 30 volts or so, is much more demanding of a disconnect. An arc, once struck, will not be extinguished by any AC zero crossing. It cannot be reasoned with, it does not know pity or remorse or fear and absolutely will not stop, ever, until it's destroyed enough equipment that the arc gap is now too wide to leap. By then, a pretty good fire may be underway. (you're gonna want to turn your sound way down, then, wait for it :) twice!) Seen it many times.

Read data sheets on disconnects and contactors but you typically see a DC rating 1/5 to 1/10 that of the AC rating, if it has a DC rating at all. I have seen a 3-phase 1200VAC contactor used for 600 VDC by wiring all 3 poles in series.

If you need a distribution panel, the Square D "QO" line, sold at Home Depot, is the only consumer panel rated for DC. Normal breakers are 48 VDC but you can special order 120VDC ones.

Harper - Reinstate Monica
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