Sizing Disconnect Switch

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Sarah78

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Need help understanding electrical disconnect switches.

I was looking at an Eaton catalog, and I don't understand why it'd only be 240VAC or 600VAC?

Why would it not be the same voltage as the line voltage going through?

Does the ampacity only matter?
 
Welcome to the forum Sarah. Perhaps it is only rated for minimum or maximum voltages. It may not be designed for a 120 volt line to go through then you'd have a empty lug (phase) As far as the 600 UL listing requires more listings related to the disconnect.

But , amps matter, too. Not just volts. Somebody else will chime in. So stay tuned. ;)
 
I believe that is the maximum voltage that can be applied to it. Use the 240V for 120, 208, and 240V systems. Use the 600V for 277, 480, and 600V systems.
 
Sarah78 said:
Need help understanding electrical disconnect switches.

I was looking at an Eaton catalog, and I don't understand why it'd only be 240VAC or 600VAC?

Why would it not be the same voltage as the line voltage going through?

Does the ampacity only matter?
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As stated above, those are maximum nominal voltage ratings. The actual voltage will be whatever is applied to it.

Yes, current matters, too. When selecting a switch, it must be rated at or above each parameter, voltage and current.
 
The other item to consider is the SCCR of the non fused disconnect switch. A non fused disconnect switch is rated at 10kA. In many studies I do, I find these switches to be overdutied (installed in a location where the fault current exceeds 10kA). The easy remedy is to install fused disconnect switches with an appropriately sized fuse and this boosts the rating to 200kA. So you need to consult a study of the system for the location you plan to install these disconnect switches.

So the ratings you need to be concerned about:
Voltage: Switch rating needs to be greater than voltage of circuit
Amp: Amp rating needs to be greater than load amps
SCCR: If non fused, short circuit at that location needs to be less than 10kA
 
Voltage ratings are based on separation of conductive elements inside of the device. 600V requires more separation than 240V does, so 240V devices can be smaller and thereby slightly less expensive. There is no reason you cannot use a 600V rated device on 240V, but you cannot use 240V rated devices on anything over 240V.
 
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