Shielded power cord, ground fault plug.

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Externet
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Shielded power cord, ground fault plug.

Post by Externet »

Hi.
A small window 120VAC air conditioner 5KBTU has its power ground fault plug with 2 equal spades, none is wider. The power cord has 4 connections to its ground fault plug : Phase, neutral, ground, shield.
There is no round grounding contact at the plug to fit the outlet.

Has that grounding round contact broken off, or is that the way is supposed to be ? Seen hair dryers with those ground fault plugs, no ground contact. But no shield.
They are supposed to work comparing current in phase wire with current in neutral wire. If dissimilar, trips. As far as I knew.

There is no continuity from shield to chassis, there is continuity from ground wire to chassis. What is this shielding doing ? New regulations ?

Enlighten, please ?
- Abolish the deciBel ! -
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Lenp
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Re: Shielded power cord, ground fault plug.

Post by Lenp »

For what it's worth...
A GFCI will work properly without a ground. Although the ground is desirable for safety it plays no part in the GFCI detection. The GFCI monitors the difference in the current between the line and neutral, and, if the imbalance is above typically 4-6 ma the circuit is interrupted. In an older house, without grounding conductors, a GFCI can be used but the outlet(s) 'must' be marked as being ungrounded.

As for the plug's ground pin, if the appliance is designed with double insulation, no metal parts are exposed that can be energized in a fault so there is no place to connect the ground, and it is omitted.

A shielded power cord is generally to surpress interference, often on computer systems. On an air conditioner, well, I see no value or need.

Regarding polarized plugs, the primary purpose is to prevent the possibility of an accessable metal component from being energized. Most typical is the case of a screw base bulb. When partly unscrewed the base's shell is exposed and that should be the neutral side of the line to prevent shocks. Single phase AC devices couldn't care less what way the power polarity is applied. It changes 50 or 60 times a second anyway, so it is really a safety issue.

Side note>
GFCI panel mounted circuit breakers can often be a bad choice if they supply circuits in a damp environment, like outdoors. If the wiring is old, or a bit of moisture permeates the wiring, they will nusiance trip. We want to protect the user, and not the small and often 'normal' cable leakage. GFCI outlets are a better choice since they protect the user and are immune to upstram cable leakage.
Len

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haklesup
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Re: Shielded power cord, ground fault plug.

Post by haklesup »

sounds like you are saying the A/C has a cord with GFCI built into it and you don't understand why there is no safety ground prong or polarization on the GFCI plug.

While most cords of this type I have seen do have all 3 prongs and polarization, ground and polarization isn't really necessary since any unbalanced current would trip the breaker on the cord not needing to rely on any path into the house wiring. so if failure current runs through the local safety ground in the cord (I think the shield is just a shield) some of that current is now not balancing in the line neutral and the cord should trip off. I think GFCI is now required by code for AC and putting it on the cord alleviates homeowners from upgrading the plug which is beyond the ability of many. I don't think you can completely double insulate an AC.
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