contactor ahead of residential subpanel question

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mark thomas

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Is there any issue with installing a contactor, controlled by a keyed switch, ahead of a 60 amp garage subpanel? The goal is to prevent unauthorized persons (eg, kids) from energizing subpanel and stuff like woodworking equipment, for safety purposes. Garage lights and some general-purpose receptacles are on house main panel and thus independent. (I know a manual disconnect with padlock would be a bit cheaper, but slightly less convenient.)
 
Not a bad idea. In the past we have installed contactors (mechanically held) to feed lighting panels that are switched off and on by a time clock.
 
if doing that, I would take it one step further and use a momentary NO keyswitch and a NC 'off' button. This way, you have an Estop button, and you would have a manual reset after a power interruption which would prevent machinery from starting unexpectedly.
 
I completely understand what you said; it's a great statement in itself!

wireguru said:
if doing that, I would take it one step further and use a momentary NO keyswitch and a NC 'off' button.
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As you described, wouldn't that be required at each machine? Isn't it always the cause where (with modern machines) some human interaction needs to happen to turn on any machinery, anyways?

This way, you have an Estop button, and you would have a manual reset after a power interruption which would prevent machinery from starting unexpectedly.
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I frankly kept thinking of all the possible variables and combinations that might be dictated by what's on site / budget / and verses of course what?s required by scope as to what they can pay for.

Another example could be:
Since the OP is worried about unautorized entry, what about timed motion sensors that can close off the power to machines, turns on lights, cause alarm to sound, or video to record, etc, etc...

Just thinking aloud, or as another poster says, "Don't listen to me I might be wrong"! :)
 
cadpoint said:
I completely understand what you said; it's a great statement in itself!



As you described, wouldn't that be required at each machine? Isn't it always the cause where (with modern machines) some human interaction needs to happen to turn on any machinery, anyways?




I frankly kept thinking of all the possible variables and combinations that might be dictated by what's on site / budget / and verses of course what?s required by scope as to what they can pay for.

Another example could be:
Since the OP is worried about unautorized entry, what about timed motion sensors that can close off the power to machines, turns on lights, cause alarm to sound, or video to record, etc, etc...

Just thinking aloud, or as another poster says, "Don't listen to me I might be wrong"! :)
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thats true: where do you stop? You could have a thumbprint scanner to turn it on...but its prudent to draw the line at what's resonable. My suggestion adds one switch only, so the cost is pretty much nothing ($6?)

As far as machinery restarting, there are all sorts of table saws, drill presses, bench grinders, etc with a mechanical on-off switch, and would come on when power is reapplied.
 
The contactor idea is a good one but cost wise a simple non fused disconnect with a pad lock will be much cheaper.
 
iwire said:
The contactor idea is a good one but cost wise a simple non fused disconnect with a pad lock will be much cheaper.
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a bit cheaper, but I am liking the contactor much better for the application. The switch requires actively locking it after turning off. With the momentary keyswitch + NC off button, when off button is pressed power is off and cant be turned back on without the key.
 
wireguru said:
a bit cheaper, but I am liking the contactor much better for the application. The switch requires actively locking it after turning off. With the momentary keyswitch + NC off button, when off button is pressed power is off and cant be turned back on without the key.
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A 'bit cheaper'? have you priced 60 to 100 amp contactors recently?

Either way it takes action on the part of the last user to either push the button or lock the disco.


To me the OPs post sound like a home garage with woodworking equipment, not a school shop that needs an EPO.

Sometimes the simple solution is the best solution.
 
mark thomas said:
Garage lights and some general-purpose receptacles are on house main panel and thus independent. (I know a manual disconnect with padlock would be a bit cheaper, but slightly less convenient.)
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Am I missing something? You can have a sub panel AND individual circuits run to a garage? Nobody mentioned it yet so I can only assume it's an attached garage.
 
It's allowed, by the code, Branch and a three wire for a light, someone else can state the Code and the recent thread link... if this is a private garage.
 
cadpoint said:
It's allowed, by the code, Branch and a three wire for a light, someone else can state the Code and the recent thread link... if this is a private garage.
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I believe what your refering to is Article 225.30(D) which permits an additional branch circuit for control of outside lights from multiple locations. The OP is talking about additional lights and receptalcles.

Also, this is a feeder and not a branch circuit. I'm thinking this must be an attached garage.
 
From the OP "Garage lights and some general-purpose receptacles are on house main panel and thus independent."

If it was just lights then I'd Correct as I answered, Forgotting the whole Thread I'm NOT correct!!!

This situation should be addressed, IMO

GOOD catch, I forgot the Complete statement of the OP, Thank You!
 
To clarify, re: cadpoint's questions, I'm not really concerned about unauthorized entry, but rather unauthorized (especially unsupervised) powering of machines. In fact, if entry were controlled/restricted, I would not need to control machines. Entry is in fact largely un-restricted.

The situation is attached garage. This is actually my own house (not a paying job!) Garage functions as hobby shop for me, and also supports kid crafts, education, etc. I don't want to keep my kids (now three year old twins) out of the shop -- to the contrary, I want them to develop interest in the stuff. But I want them to be safe of course. I can and do teach them safety and boundaries, but just like in industry, it's better to have not just good practices, but some controls as well. I am also thinking ahead to when random kids are around (neighbors, kids' friends, etc.) I have about a dozen or so machines that are potentially hazardous by merely throwing the power switch -- lathe, milling machine, grinder, buffer, band saw, table saw, etc.

I have a 125 amp subpanel that serves about half my house installed in my kitchen, about three feet from garage. This subpanel has three circuits feeding garage. One feeds a half dozen receptacles in the garage, to which no tools/machines are connected. This is for general utility (vacuum, glue gun, radio, etc.) like any garage would have. A second circuit for garage lights. The third is a 60 amp that feeds another subpanel in the garage itself. This is where I am planning to put the contactor. This panel feeds receptacles in the garage that will be used for machines and tools. Fwiw, this garage panel also feeds a phase converter, which in turn feeds a 3 phase panel in the garage, which has circuits to the 3 phase machines and receptacles. In other words, my garage has 120v receptacles, 240v receptacles, and 3P/240v receptacles -- not the average garage.

I plan to install a key lock that energizes the garage subpanel, using the type where the key is not removable while switch is on. I will put the key on my keychain with car and house keys. This way, I'll never get in my car and drive away leaving the garage energized...

Because the garage has permanently energized receptacles, this setup is not foolproof, that is, it doesn't prevent someone from taking a tool and plugging it into the always-on receptacles (just like a regular garage) However, virtually all the stationary tools are 220v or 3 phase, and the always-on stuff is only 120v. So while someone can get a hand drill out and plug it in (well, most are cordless, but you get the point) no one can fire up the 10HP lathe without the key. And no one should be doing that without me being there.

Btw, my AHJ has no specific problems with all this, other than finding the whole thing, including me, rather wacky. I think the thing that most surprised them was that I sought to permit it! But given my experience, I don't view AHJ's OK as a lot of validation, so I thought I'd ask if anyone here saw any "issues" with this.
 
How about a shunt trip circuit breaker? Do they make those for resi panels? You'd need to go to the main panel though to turn it back on.
 
Why not just add a lock kit from the panel's manufacturer? Assuming the subpanel has a door, simple,cheap,& easy. My shop has 2 panelboards, 1 for lighting, & 1 w/ a backfed main for all the receptacles/tools/air compressor that could be locked if desired.....
 
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