[Amps] 4 wire 240VAC service? What to do now?

[Jim Brown]

On 4/4/2011 12:22 PM, TexasRF at aol.com wrote:
> In a typical sub panel, is the buss bar that is used to common the 
> neutral leads insulated from the box chassis? I have installed a 
> couple of sub panels through the years but never paid any attention to 
> that.

All panels are built with a neutral bus that is insulated from the steel 
enclosure. In most, there is a large bonding screw that shorts the 
neutral bus to the enclosure.  If the neutral bond is not permitted, 
this screw must be removed.  Not all electricians know that this 
matters, but it is critical. Indeed, extra neutral-to-ground bonds are 
one of the most common wiring mistake in buildings.

An easy way to sniff for this is with an AC voltmeter that has a good 
low volts scale. Connecting the meter between ground and neutral any 
where in the system except at the bonding point, you should see some 
small voltage, typically less than a volt or so. If you see zero, 
there's a neutral to ground short close by.

73, Jim Brown K9YC