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Fused Safety switch for RPC

Hobby Shop

Stainless
Joined
Mar 20, 2014
Location
Michigan
Hi guys. I’m almost at the finish line with the new shop.

I’ve read a lot of posts about needing to protect the RPC idler motor with an overload relay. I’m somewhat challenged in this department and would like something that’s somewhat plug and play.

Ideally, I’d like to install a 3 phase 50amp breaker but I haven’t seen any without having to buy a 100amp service panel. I have seen some 50amp fused disconnects that sell fairly cheap.

Is it ok to use a fused disconnect for the RPC idler motor protection?

This is my set up.

1) Phase Craft 20 HP RPC being fed with 100amp single phase breaker.
2) RPC feeding 3 phase service panel
3) 3phase power surface mounted to machines.

All the machines have a fused disconnects and some have overload relays.

Any help is appreciated.
Andy
 

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Hi guys. I’m almost at the finish line with the new shop.

I’ve read a lot of posts about needing to protect the RPC idler motor with an overload relay. I’m somewhat challenged in this department and would like something that’s somewhat plug and play.

Ideally, I’d like to install a 3 phase 50amp breaker but I haven’t seen any without having to buy a 100amp service panel. I have seen some 50amp fused disconnects that sell fairly cheap.

Is it ok to use a fused disconnect for the RPC idler motor protection?

This is my set up.

1) Phase Craft 20 HP RPC being fed with 100amp single phase breaker.
2) RPC feeding 3 phase service panel
3) 3phase power surface mounted to machines.

All the machines have a fused disconnects and some have overload relays.

Any help is appreciated.
Andy

200 A Service entrance panel, 60A breakers, 10 HP Phase-Craft, 2 each 10 HP Phase Perfect, one 3-Phase distribution load center downstream of each, rotary lockable disconnect each machine, protection IN/ON it per its nature.

We we are on the same wavelength. My "chunks" are just half the size of your ones.

Pro: The utility mains side is but split-phase, not 3-Phase.

Accordingly supplementary load centers, their main and load breakers - such as the 100A you mention, cost way less than half what each of my independent 60A Square-D fused disconnects did - even bought used.

Con: Those cheap and common load centers do not ordinarily have a "lockout" feature built-in, load OR main breaker.

The fused-disconnect ones do have lockout.

I'm sure that is not the only way to "meet Code", there's lots more involved anyway.

But having a lockout there, as well as another at each load surely doesn't hurt, either.

Used-but-good units from NRI, also NOS from others among the "usual suspects" have eased the other pain - the one in the wallet!

Mine is not just surface-mount runs. The whole rig is done to be easily removable and portable to a new facility.. and NOT make this shop look a mad scientist's lab kludge when the house someday goes to be sold to "ordinary" residenters who just want to park a motorcar there.

:)
 
You can install a 3 pole breaker in your 3Φ panel and backfeed it. Wire the RPC output to the breaker load side, and use it as the panel main.

SAF Ω
 
Thanks for the help guys.

I’ll talk it over with my electrician and see how he feels about back feeding the panel. I’m just a one man shop
so I don't think there should be any issues.

The 20hp idler motor nameplate says it’s 48.0 amps, should I size it with a 50amp breaker or does it get bumped up to 60amps?
 
For short circuit protection on the input side of the converter motor, your allowed to go up to 250% max, with a inverse time breaker.

For the overload protection of the RPC motor, 125% is the maximum size allowed for a motor with a 1.15 service factor.

50A would give you tighter protection, if you don't need the maximum capacity. 60A would be the maximum for your 1.15 SF motor.

A motor starter with overload protection built in would give you better protection than a breaker or fuses, you would need a size 3 starter for your 20HP motor, with an overload relay heaters to match your nameplate amps.

SAF Ω
 








 
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