Grounding Metal Outlet Boxes and Isolated Ground Receptacles

isolated ground screw on the Furutech.

Please explain. I didn’t know Furutech made an isolated ground (IG) type receptacle.

A true isolated grounding type receptacle has the metal supporting back strap of the receptacle insulated from the "U" shaped ground contact of the receptacle. The green equipment ground screw on the receptacle is connected only to the "U" shaped ground contact. An insulated green equipment grounding conductor, wire, connects to the green equipment ground screw and is ran with the branch circuit wiring, and connects to the ground bus in the electrical panel.

If the receptacle is truly an IG receptacle NEC requires the receptacle to have an orange triangle on the front face plate. Or the face plate might be entirely orange with a triangle.

Example:

http://www.graybar.com/store/en/gb/2-pole-3-wire-heavy-duty-duplex-receptacle-isolated-ground-20a-12...

If the Furutech is not an IG duplex receptacle then you wasted your money installing a 3 wire with ground, I assume NM-B cable. (Romex is a trade name of NM-B)

Not only did you waste your money you may find the hot and neutral current carrying conductors of the branch circuits will induce a small voltage onto the equipment ground wires. The induced voltage can cause ground loop hum.

You should have used 2 wire with ground NM-B cable.

Example of 6-2 with ground:

https://www.wireandcableyourway.com/6-2-w-g-nm-b-wire-black.html

Notice the bare equipment grounding conductor, wire, is in the middle between the Hot and neutral wires? The magnetic fields of the hot and neutral wires cancel each other out. With 6-4 wire because of the geometry, lay, of the wires inside the outer sheath, jacket, the 2 equipment ground wires you have are more likely to pick up an induced voltage by the hot or neutral or both. You may find the 6-2 with ground NM-B is 3 wires ran in a slight tight spiral twist as well.

http://centralindianaaes.files.wordpress.com/2012/09/indy-aes-2012-seminar-w-notes-v1-0.pdf

Next:

http://www.middleatlantic.com/resources/white-papers.aspx

Addendum to Power Distribution White Paper (87 KB)

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As for the metal box. Many guys have experimented using metal and plastic boxes. There have been mixed opinions on the subject. There was an EE on Audio Asylum that ran some kind of tests and from his results he recommended plastic over steel.

Here is one of his posts regarding steel boxes.

http://www.audioasylum.com/audio/tweaks/messages/16/165520.html

I believe Albert Porter, an Agon member, did some tests as well, just going from memory, and he went with plastic boxes for his dedicated circuits as well.

Have you covered everything with drywall yet?

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stickman451 said:

I will contact Furutech distributor to confirm whether not the outlets are truly ’isolated’ ground and go from there.

I assume Furutech receptacles are Listed by a recognized third party testing laboratory, such as UL.

If the duplex receptacle is an IG, Isolated Ground, per NEC it will have a triangle near the "U" shaped ground contact hole.

Here are a couple more pictures of IG duplex receptacles.

https://www.grainger.com/product/HUBBELL-WIRING-DEVICE-KELLEMS-Duplex-Flush-Receptacles-WP6064708/_/...

https://www.zoro.com/search?q=Isolated+Ground+Receptacles&gclid=CPmd0r_0oNACFQiUaQodSSoOxg&g...

At the time the electrician looked at the job with you, you must not have had the duplexes to show him. You must have just told him they were IG receptacles. That is the only reason the electrician should have installed 4 wire branch circuit wiring for a 120V dedicated circuit. By code he needed a second equipment ground wire for the metal box. (Unless the branch circuit raceway is hard metallic metal conduit like EMT (thin wall) for example, then the box ground can be the conduit per NEC providing it is a continuous run from the box to the electrical panel. The conduit can connect to other electrical metal boxes along its’ way to the electrical panel.)

Is the wire 6-3 with ground NM-B cable, Romex? If so, there is no reason to ever use an IG receptacle when NM-B cable is used.

Just a guess the electrician used steel boxes because of the #6 wire you wanted him to install. Just a guess he installed a deep 1900, 4" x 4" X 2 1/8" deep box, with a 1 gang raised device cover, for a single duplex receptacle. He may have needed the bigger box to meet the percentage of fill required by NEC for the #6 wire.

Have you ever watched the Cary Grant movie, Mr. Blandings Builds His Dream House ?

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