ECN Forum Forums General Topics of the Trade General Discussion Area GFI protection of cooktop

Trumpy,

I don't know what an RCD is. Also I would have to concede to anybody's experience with GFI's on a ranges because I've never done it.

But I can say that leakage current is what a GFCI is for. If you have leakage current but you decide it is ok, well, I don't know how to address that.

Amp-Man,

[1] You are not required to use GFI protection.

[2] I think you are misinterpreting the purpose of the EGC. Are you expecting it to protect a human from a shock hazard in the presence of leakage current?

Physis,

I'm aware that GFI protection is not required in this case (well, there is the issue of the cooktop not being listed for outdoor use); and yes, grounding the non-current carrying parts of a tool or appliance is exactly what I think an EGC is for.

By grounding I mean keeping the non-current carrying metal parts of the equipment at zero (earth) potential, so that there is virtually no chance of shock or electrocution. This is accomplished by providing, via the EGC, a path back to the source for anything from leakage current to a dead short.

And yes, I know that the current will divide among any and all paths available. With a solid EGC, though, there's virtually no chance of getting hazardous current through a person.

It appears that you think the only way to accomplish personnel protection against shock or electrocution from stray current is with a GFCI. I disagree; the EGC was used for that purpose for decades before GFCI technology became available.

I am aware that the GFCI offers advantages over a grounding receptacle outlet. For instance, in a branch circuit with multiple and poorly made EGC splices, the impedance of the equipment grounding path may be high. High enough, in some cases, that a person begins to represent a sufficiently low-impedance parallel path that dangerous current may pass through the person.

Also, in a cord-and-plug connected appliance or tool, the EGC may easily be (and often is) defeated by improper use of an adapter, or by cutting off the plug's grounding pin. Sometimes, the cord is damaged, compromising the EGC in the cord. That's why GFCIs are required to protect cord-and-plug connected equipment in locations where a person is likely to present a good return path for stray energy.

Conversely, that's why there are few requirements that hard-wired equipment be GFCI-protected. There's no cord or plug to be damaged or tampered with; there's no cordset to be damaged; and, with the typical dedicated circuit for a fixed appliance, the EGC usually has fewer splices (and there's a lot less opportunity for EGC splices to be tampered with).

The other reason for not requiring hard-wired equipment to be GFCI-protected (except for spas, hot tubs, etc) is leakage current. For instance, fixed electric outdoor deicing and snow melting equipment is required to have GFPE (ground fault for protection of equipment, tripping at more than 6 mA and less than 50mA) protection, because a GFCI is likely to trip from leakage current.

Leakage current is not an inherent danger; it's when there's no good equipment grounding pathway that it's a problem, and that's what GFCIs are for. GFCIs are a great safety device, but they're not a panacea.

Cliff

[This message has been edited by amp-man (edited 01-05-2005).]

[This message has been edited by amp-man (edited 01-05-2005).]

Amp-Man

You are at least right about one thing.

I do have a preference for GFCI protection whether it is required or not.

Can I ask you a hypothetical question?

If you are standing bare foot on a well grounded concrete slab, that is wet, and has an ungrounded conductor laying on it.

Is that EGC that is at the same potential as the slab going to be useful in preventing you from getting shocked?

And if so, how?

Physis,

Ah, now I'm beginning to understand your point of view. You appear to be concerned about a person coming into direct contact with an ungrounded conductor.

You're absolutely right, an equipment grounding system won't do any good there, because there isn't any equipment in the picture. A GFCI will reduce the chance of shock or electrocution in your scenario--contact with a hot wire.

But I'm talking about a situation involving a piece of utilization equipment, specifically a cooktop.

I'm talking about the normal use of the cooktop, where due to the appliance design, there is virtually no chance of a person coming into direct contact with an ungrounded conductor.

What the equipment grounding system is designed to do is keep the case, frame, or other normally non-current carrying metallic parts of the tool or appliance (or whatever) at ground potential.

Unless you're working on the wiring, or there's serious damage to the appliance, you aren't going to come into contact with an ungrounded condictor. You are however, very likely going to come into contact with the metal case of a drill, or the frame or case of a washing machine, or the like. That's why those things are grounded--that is, connected to the EGC.

If your objective is to reduce the chance of injury from contacting an ungrounded conductor, then GFCI-protection is the way to go. I'm not arguing against GFCI protection of receptacle outlets as required by the Code.

I just think the chances of the homeowner or appliance user contacting an ungrounded conductor on a hard-wired appliance circuit are essentially nil, and therefore (IF the cooktop were being used as listed) there'd be no benefit to using a GFCI.

Thanks for taking the time to discuss this. I do appreciate your perspective, and have learned from it.

Cheers,

Cliff

Cliff, go back to my first post and reconsider.

I'm glad that you don't seem so offended now.

Again though, If it were up to me there'd be GFI's everywhere.

Edit: you only have to contact the water.

[This message has been edited by Physis (edited 01-05-2005).]

Cliff I also agree a GFCI is not required for this application.

However just because something is grounded does not exclude it from GFCI requirements.

Think of the GFCI as a back up to the EGC.

The GFCI rule that went into the 2002 NEC for commercial kitchens is a good example of this.

All 120 volt 15 and 20 amp outlets must in commercial kitchens must have GFCI protection.

That rule went in as people had been killed by appliances that the EGC failed on.

Another example is the 2005 NEC requirement that vending machines have GFCI protection again it is a back up to the required EGC.

This is all for plug and cord connected appliances, hardwired and the GFCI regiments do not apply.

Same for a pool pump for that mater.

Bob

Personally, I'd never fail to protect a piece of Electrical Gear that is installed outside, with an Earth Leakage Circuit Breaker.
The risk is just too great where Moisture is a variable in the equation.

THIS IS ONLY A THOUGHT EXPERIMENT

DON'T EVER DO THIS:

Fill up a bath tub and throw in any properly grounded appliance.

When you DON'T STICK YOUR FINGER IN THE WATER.

Why can you still get electrocuted when it's properly grounded and you haven't touched any conductors?