[Jukebox-list] Jukebox Wiring Question - switched and fused neutral

[Jay Hennigan]

Jimmy Day wrote:

> As for the GFI receptacle, I have not seen any with only two wires. The 
> ones in hair dryers are actually part of the unit and are not designed 
> to power anything else. AFAIK, two-wire GFIs are not available for new 
> construction, and if one feels that a GFI does not need to be grounded 
> should see what their local electrical inspector thinks ;-) 

The electrical inspector *SHOULD* think that it's an excellent idea as 
long as there is a sticker saying "No Equipment Ground" on the GFI. 
Such stickers are included in the packaging of GFIs for this very purpose.

NEC 406.3(D)(3)(b) "Where no grounding means exists at an outlet box, a 
non-grounding receptacle may be replaced with a grounding-type GFI 
receptacle with no ground connection. The receptacle must be marked "No 
Equipment Ground". If the GFI protects additional loads, a ground wire 
must not be connected to the supplied loads."

http://www.naturalhandyman.com/iip/infelectrical/infgfi.html#7

> Using one 
> inside a jukebox is of questionable benefit. What we are concerned about 
> is leakage to the metal parts; for example, an old cracked fluorescent 
> socket or the brittle wiring in an old AMI possibly touching the metal 
> chassis. A regular 3-wire GFI would sense current in the ground circuit 
> and immediately trip. A 2-wire one may not, since it is not "looking" at 
> the ground circuit.

But the old AMI has no ground circuit.  It has just a two-wire cord.

Single-phase GFIs are by nature two-wire devices.  They accommodate the 
ground pin on three-wire cords and bond it to the frame, but the ground 
pin is not electrically connected to any of the active circuitry within 
the GFI.

The purpose of a GFI isn't to protect equipment, but people.  Fuses and 
circuit breakers protect equipment.

In your example above, the brittle wiring in an old AMI allows an 
exposed hot wire to touch the metal chassis.  The chassis is now at 120 
volts AC.  The jukebox keeps playing.  Next, a person standing on a wet 
floor clutching a nickel touches the metal coin slot on the jukebox. 
The GFI now senses that more current is leaving the hot wire than is 
returning via the neutral (as current is now flowing through the nickel, 
the person, and the floor back to ground).  The person receives a very 
brief shock and the GFI trips within a few milliseconds, disconnecting 
power.

So, a two wire cord either with a built-in GFI, a GFI inside the jukebox 
connected directly to the main cord, or replacing the wall outlet 
feeding the jukebox with a GFI are all good ideas.

> The GFI receptacles one finds at the supply houses do have a ground 
> connection.   I have also installed GFI breakers in the main electrical
> box. These breakers, unlike regular breakers, MUST be grounded to work. 
> "Ground Fault Interrupter" - it trips if it detects ANY current 
> difference between any of the three wires.

Not true.  The ones in the breaker box do require that the neutral 
toward the load be extended through the GFI, and not tied to the common 
neutral block in the box.  Single-phase GFIs are two-wire devices.

> This is why we are getting our newbies confused. One says to use a 
> three-wire cord, another says no, that is not safe unless it is done a 
> certain way, someone else says yes it is safe but it must be connected 
> so and so, etc, etc. I would be confused too!



--
Jay Hennigan - CCIE #7880 - Network Engineering - jay at impulse.net
Impulse Internet Service  -  http://www.impulse.net/
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