508 panel 480 disconnect at machine or at power source

[3tech]

Can I have fuses on the panel and require the customer to supply power with a shutoff switch? The panel would be 480 3 phase and controls a 3HP pump and a 25K watt heater with 24vac control circuit. Currently UL has aproved our panels 240vac with a miniture circuit breaker on the Electical box accessed from the outside and no disconnect switch.

 

[jraef]

I think that someone at UL may have grossly misrepresented what your panel is "listed" for. Mini Circuit Breakers (MCBs) are NOT suitable for any more than 10kAIC, a few brands are maybe 18kAIC, but in the vast majority of 480V industrial installations, the available fault current is a lot more than 10kA. I would therefore think that fusing with Current Limiting fuses is an absolute must.

By the way, I know of no MCBs that are rated for 480V other than as 480/277V, so they MUST have a 4 wire installation, including a neutral landing lug in the panel. They are NOT suitable for use in 480V delta installations at all. You should be vry careful about what you tell your users about how and where they can use those things.

Salesmen are selling these things to panel builders without truly understanding their limitations, and some people are using them without reading all the fine print.

 

[DRWeig]

3tech,

First of all, please heed jraef's points, all valid.

That said, my read of 508A allows remote location of the disconnecting means (exception to 30.3.1) provided that the panel is labeled at the point of supply connection in accordance with 60.1. Markings need to be complete and un-ambiguous, including size, and the fact that the disconnect needs to be provided by the installer.

Let us know what works!

Good on ya,

Goober Dave

 

[3tech]

All good points, thank you! jraef you are right the Mini Circuit Breaker I am using now on the 240vac unit has nothing for 480, and nothing mini about the type of circuit breaker needed including cost as I understand it the customer will need a Molded Case Circuit Breaker.

What I plan to do is label the box the panel goes into, per 508A 60.1 (the panel is used in a end product of ours, a tank that circulates heated water) stating the size, and type of circuit breaker and disconnect needed.

The machine will come with with 3 wire with ground SO cord to hook up to the circuit breaker. Is there anything I should look out for in doing this? Thank you again.

 

[DRWeig]

Hmmmm....

Read section 28 of 508A thoroughly regarding your cord, it can be done -- but all the rules for sizing and relieving strain must be followed (and the cord needs to be listed UL 62).

I don't think you can do cord-connected without including a UL plug on the end of it. Cord connection directly to a breaker isn't an option, at least the way I read it. By using a cord, you're designating your panel as portable.

Good on ya,

Goober Dave