External disconnect

[SAP]

Can a standard external disconnect that only says 240,60 hertz, Can I use for 240 volt dc, our can I only use for AC, can you pleas give me a code reference, I'm thinking you can only use for AC thanks, it's a debate I got with another co worker, I don't have my code book on me, I got 1000$ Bet riding on this...... Thanks

 

[ron]

Code says to use equipment per its listing. DC is 0hz, so if it says 60hz, then no good.

 

[ggunn]

Can a standard external disconnect that only says 240,60 hertz, Can I use for 240 volt dc, our can I only use for AC, can you pleas give me a code reference, I'm thinking you can only use for AC thanks, it's a debate I got with another co worker, I don't have my code book on me, I got 1000$ Bet riding on this...... Thanks

Check the data sheet for the disco. Some are listed for both AC and DC, some are not, and those that are dual listed often have different voltage tolerances. If it's not listed for DC, you cannot use it for DC.

 

[Carultch]

Can a standard external disconnect that only says 240,60 hertz, Can I use for 240 volt dc, our can I only use for AC, can you pleas give me a code reference, I'm thinking you can only use for AC thanks, it's a debate I got with another co worker, I don't have my code book on me, I got 1000$ Bet riding on this...... Thanks

Most standard AC disconnects can either work at 50 Hz or 60 Hz, but few standard AC disconnects can work for DC. Because it is inherently more difficult to suppress the arc, as you draw the blades apart, when the blades are continuously energized at a constant voltage, instead of a voltage that periodically crosses zero.

Some DC disconnects will work by design as AC disconnects, with no derates. Because DC is more difficult to break than AC. However, others may be polarity sensitive based on the way that they supress the arc, which means they couldn't work for AC.

You need to check manufacturer's information on whether you can make it work, and if so, how. Some require that you only take credit for a fraction of the ampere rating, or that the DC voltage rating is significantly less than the AC voltage rating (for instance, 250V instead of 600V). Some require that you series the blades together, so that the full voltage is distributed across them. Square D has a data bulletin about this, where they indicate that 2 blades in series is enough to get the full volt and current rating out of the unit as a whole. Other manufacturers usually require 3 blades in series.

 

[jaggedben]

In my experience if you want a general duty type disco that's rated for DC you probably need a 600V rated switch. Square D's line of 600V switches are rated for both AC and DC. Eaton has some too. Not to say it doesn't exist, but I don't think I've seen a regular 240V disco that's listed for DC.

 

[Carultch]

In my experience if you want a general duty type disco that's rated for DC you probably need a 600V rated switch. Square D's line of 600V switches are rated for both AC and DC. Eaton has some too. Not to say it doesn't exist, but I don't think I've seen a regular 240V disco that's listed for DC.

General duty is 240V and below, by design. 600V of anything would have to be heavy duty.

Square D switches are only rated at the full voltage & current rating, if you connect two poles in series.

 

[jaggedben]

General duty is 240V and below, by design. 600V of anything would have to be heavy duty.

I think such terminology varies slightly among manufacturers, but I should have used different wording. What I really meant was switches that your local electrical suppliers are likely to have in stock.

Square D switches are only rated at the full voltage & current rating, if you connect two poles in series.

Yes although if you're disconnecting both conductors of an ungrounded string then at least some people consider that the same thing. And on the sq-d switches, it has to be the 2 outside poles of the 3 pole switch.

 

[ggunn]

Yes although if you're disconnecting both conductors of an ungrounded string then at least some people consider that the same thing. And on the sq-d switches, it has to be the 2 outside poles of the 3 pole switch.

True, that's the way SqD and Eaton look at it. You are breaking a series circuit in two places; the two places need not be adjacent.

 

[kwired]

In my experience if you want a general duty type disco that's rated for DC you probably need a 600V rated switch. Square D's line of 600V switches are rated for both AC and DC. Eaton has some too. Not to say it doesn't exist, but I don't think I've seen a regular 240V disco that's listed for DC.

Seem to recall most that are marked 600 VAC that also are marked for DC are only rated for 250 VDC.