120/240 GFCI Requirement

[wedlock]

I am not an electrician; I'm an electrical engineer and am working on an article entitled "Efficient Shop Wiring". I need some GFCI advice.

The goal is to use a single 3-wire cable to provide 120/240 to wood shop wall boxes. Since shops are often in garages or "unfinished" basements, it is my understanding that the 120V outlets require GFCI receptacles. I know each 120V receptacle must be GFCI and not fed "downstream" from a single GFCI with this arrangement. Is there a requirement for GFCI for the 240V receptacles used for machinery connections?

Thanks for you help an patience!

Bruce

 

[earlydean]

Re: 120/240 GFCI Requirement

I am an electrician, and I always protect the downstream receptacles with the first GFCI receptacle in the garage (and everywhere else too). Where do you get the idea you can't?

 

[iwire]

Re: 120/240 GFCI Requirement

You are trying to do something in a most unusually way.

As a general rule it is safer to do things the more accepted way so when people come to service this installation they will know what is happening.

I am guessing your thought here is that a home work shop has only one worker so you are not concerned with overloading the one breaker feeding this set up.

I will post the code rule for GFCIs in basements below but the short version is 15 and 20 amp 120 volt receptacles must have GFCI protection.

You have a few options.

1)Install a 2 pole 120/240 GFCI breaker at the panel and protect both the 120 and 240 outlets.

2)Use a standard 2 pole breaker at the panel go to your 240 outlets first then install a GFCI outlet at the first two (each leg of the 3 wire cable) 120 receptacles and protect all receptacles down line with those GFCIs

3)Use a standard two pole breaker at the panel and go in any order with the 120 and 240 outlets but install a GFCI outlet at each 120 volt location.

IMO keep the 240 outlets on a separate breaker, by the time you jump through hoops to do this you will have spent as much as running a 2 wire home run for the 240 outlets.

Here is the code rule.

210.8(A) Dwelling Units.
All 125-volt, single-phase, 15- and 20-ampere receptacles installed in the locations specified in (1) through (8) shall have ground-fault circuit-interrupter protection for personnel.

(5)Unfinished basements ? for purposes of this section, unfinished basements are defined as portions or areas of the basement not intended as habitable rooms and limited to storage areas, work areas, and the like

Exception No. 1: Receptacles that are not readily accessible.

Exception No. 2: A single receptacle or a duplex receptacle for two appliances located within dedicated space for each appliance that, in normal use, is not easily moved from one place to another and that is cord-and-plug connected in accordance with 400.7(A)(6), (A)(7), or (A)(8).

Exception No. 3: A receptacle supplying only a permanently installed fire alarm or burglar alarm system shall not be required to have ground-fault circuit-interrupter protection.

 

[wedlock]

Re: 120/240 GFCI Requirement

My objective is to use two-gang wall boxes with each furnished with a 120V duplex and a 240V duplex receptacle. This is a one-man shop, so one circuit is sufficient as only one machine is in use at a time. I have pulled a single 3-conductor cable through my finished shop walls, and everything works fine. In fact, I also control my central dust collection system by sensing machine current (red conductor) at the breaker and using that to switch power to the dust collector motor. So when a machine is turned on and off, the dust collector comes on and off automatically. The 120V receptacles are fed from the black wire, so their current doesn't control the dust collector. Actually, I do feed the 120V chop saw and router table from the red so they do control the dust collector, too.

The advantage is you only have to pull one cable, and the boxes are less cluttered with only four conductors entering and leaving rather than the six you would have with a pair of 2-conductor cables, one for 120V and one for 240V. I am planning to write this up for publication, so I need to cover the GFCI requirement.

The 120V GFCI requirement can be satisfied by using a 120V GFCI outlet at each receptacle location; the usual "downstream" connection will not work since it depends on a current balance in the hot and neutral conductors to the downstream receptacles. When a 240V machine is turned on, the 120V GFCI will trip because of the current imbalance in the downstream hot and neutral conductors. But using a GFCI for each 120V receptacle will work.

Similarly, using a 240V GFCI breaker will not work either since when a 120V load is applied, the current will not balance in the two hot conductors, tripping the breaker.

My basement shop is old work (previously a finished room with a rug) with finished walls but an epoxy painted cement floor. If it were new work, I would use separate conductors for 120V and 240V, each protected with a GFCI breaker, but I'd probably need to use separate boxes for 120V and 240V with the extra wire as mentioned above.

The question really is, does the code require GFCI protection for 240V receptacles? If not, then this system, while not a standard wiring plan, appears to meet the code. If 240V receptacles require GFCI protection, then it will not meet code. A publisher will certainly ask that question.

Bruce

 

[david]

Re: 120/240 GFCI Requirement

Bruce

First, welcome to the forum, most of us like electrical engineers. We are all here to learn.
Second notice Bob said a 240/120- volt GFCI breaker not a 240- volt GFCI breaker.

The code reference Bob gave you included 120-volt rec. not 240 volt rec. and he was wanting you I take from that that 240 volt rec. where not required to be GFCI protected. For that matter look at exception # 2 and decide if your installation falls under that exception. Remember you can still provide the GFCI protection even if the CODE does not require it.

 

[iwire]

Re: 120/240 GFCI Requirement

Originally posted by wedlock:
Similarly, using a 240V GFCI breaker will not work either since when a 120V load is applied, the current will not balance in the two hot conductors, tripping the breaker.

Not so if you use a 240/120 GFCI breaker.

There is a connection on the breaker for line to neutral loads.

I do agree that down streaming the outlets from a GFCI will not work the way you have run your circuit.

There is no requirement to protect the 240 outlets with a GFCI.

The advantage is you only have to pull one cable, and the boxes are less cluttered with only four conductors entering and leaving rather than the six you would have with a pair of 2-conductor cables, one for 120V and one for 240V.

We are electricians and we are well aware of what it means to run separate circuits and box fill requirements.

The fact is we do it all the time and IMO you are trying to reinvent the wheel.

I am planning to write this up for publication, so I need to cover the GFCI requirement.

Do you carry liability insurance?

I am not being a wise guy I am dead on serious.

You tell people how to do this and they get hurt be prepared.

 

[Guest]

Re: 120/240 GFCI Requirement

This project sounds ill-conceived if it's intention is to "simplify" the circuit.

Correct me if I'm wrong, but to protect simultaneous 120-volt and 240-volt receptacles from one GFI would require a contactor. The contactor would disengage if either the 120-volt or 240-volt were to fault.

The 120-volt and 240-volt will be separate loads, so in my estimation it would take separate GFCI protection to protect each load separately, or it would take one GFCI protector covering a contactor which would monitor & release both loads at once.

In a sense the 120-volt load would be a tap off the 240-volt circuit. Can this be properly protected by GFCI without a contactor?

Why not run 12-2-2 and use two circuit breakers? One for 120-volt, and one for 240-volt?

Also, having a circuit that depends on only one piece of machinery being on at a time seems short-sighted in a real world workshop environment.

I am open to all helpful comments.

 

[david]

Re: 120/240 GFCI Requirement

I reread and noticed you said 120 volt duplex Rec. not single rec. so exception 2 would not apply to you installation

 

[david]

Re: 120/240 GFCI Requirement

Bruce
You mentioned that the basement has finished walls. If the basement has finished construction the GFCI protection is no longer a code issue but a design issue.

Hope this is helping and not confusing the issue..

 

[tonyi]

Re: 120/240 GFCI Requirement

As a practical matter, using a GFCI recpt at each tool station will quickly negate any cost/labor savings from using a single run of 12-3, and a two pole 240/120 GFCI breaker that could handle this lashup correctly is very expensive. I don't know of any that independently trip either - they'll take out both legs when they pop.

A single run of the new SouthWire 12-2-2 Romex would cure all these cost issues and do what you're looking to do.

 

[wedlock]

Re: 120/240 GFCI Requirement

Wow! Thanks for all the info. You all offered some very good ideas.

I was not aware that you could get 12-2-2 Romex. Never saw it at Home Depot, but I never thought to ask at my local electrical contractor supply house. That would be one good solution.

I did search the web and asked at the supply house about 240V GFCI breakers, explaining my need. They didn't tell me a 240/120 GFCI breaker was available. Can you tell me who makes one that would fit in a Murray panel? That's an easy upgrade and would protect all my shop wiring.

Bob Badger replied that there is no requirement to protect 240V outlets with a GFCI. That also seems to be what the code says. Is that for sure correct? Just want to double check.

Again, my thanks for all your help and comments. It has been very educational for me.

Bruce

 

[tonyi]

Re: 120/240 GFCI Requirement

If you could find one, a Cutler Hammer CL220GF is a "classified" 2-pole 120/240V 20A breaker that's suitable for use in Murray panels. Expect to pay well over $100 for one though.

Siemens/Murray may make a similar product, but I don't have one of their catalogs on hand right now.