dis connected subpanel reads 4 volts @ground

I recently connected a subpanel in the shop. It is controlled by a 30 amp breaker on the main panel. When this breaker is off, and no power is at the subpanel, I read 4 volts from the ground bus bar. The subpanel is grounded to its own nec copper ground bar. The neutral wire is connected to the main panel. Does this mean that 4 volts are coming through the neutral wire?? What does that mean? Is it a problem??
Drew

 

4 volts from the ground bar to what? the hot, neutral, waterpipe?

 

If the answer to joed's question is 4 volts between the ground bus bar and the hot, then you can forget it -- it's phantom voltage. Digital voltmeters are sometimes very stupid. Measure it with an analog voltmeter and let us know what it says.

 

It is four volts between the ground and the neutral bus bar. Both hot wires show zero voltage when the breaker is off on the main panel, but the ground shows four. It seems kind of weird to me.

 

Is there an equipment grounding conductor run from the main panel to the subpanel? If not how is the subpanel grounded?
Don

 

If there is no grounding wire between panels, and if the shop is detached, and if there is no metallic path between the buildings, then the ground and neutral should be bonded at the subpanel. This of course would eliminate the 4 volts.

If all my "if"s are not true, then you may have miswired the subpanel.

 

There is a neutral wire which runs between panels, which I am assuming is grounded. There is no metallic path between the buildings which are separate.
The breaker that controls the subpanel actually is connected first to another breaker which is separate from the main panel and controls the water heater. This water heater breaker does not have a neutral or ground wire coming from (going to) the water heater to the breaker, nor from the main panel to this "sub panel" breaker. I'm not sure of the correct term.
The breaker that controls the wiring to the subpanel in the shop has a neutral wire in the neutral bus bar in the water heater breaker, and there is a bonding strap from this busbar to the box which contains the lone breaker. I'm not sure what this exactly does, since the box nor the water heater appear to be grounded. I'm sure it's a no no for the water heater, but it's a rental and the landlord won't pay for anything until it breaks!
I have connected a 5/8 copper grounding rod to #6 copper to a separate bus bar on the subpanel. I am connecting all of the bare copper ground wire to this. Is this sufficient, correct, not dangerous??
Thanks for the help,
Drew

 

Get the water heater out of the picture!!! Feed the subpanel with its own breaker. Then bond the ground and neutral at the subpanel. What you have now is very unsafe.

 

The connection to your water heater's breaker box has how many wires going to it? What color is the insulation on those wires?

If I understand your description correctly you have a enclosed breaker serving as the disconnect for your water heater. The feeder for your detached shop building is conected to that disconnect. Is it connected to the wires that supply the disconnect from the main panel or to the terminals of the breaker that supply the water heater? The circuit that supplies your water heater should not be used to supply that outbuilding unless it has a separate grounded current carrying conductor (neutral) and Equipment Grounding Conductor (EGC). It would also need to be more than thirty amperes. Your water heater does not use a grounded current carrying conductor (that most of us call a neutral) in order to work. I suspect it has only two ungrounded conductors and an EGC run to it's disconnect. Running the three wire plus ground circuit to your shop from that circuit is dangerous because the current flow from part of the 120 volt loads in your shop will be flowing on the EGC of the water heater circuit. That current can also flow in any metallic plumbing that is attached to your water heater. The flow of current over these unintended pathways can lead to heating, arcing, and thus fire! If anything goes wrong with the connections in the water heater circuits EGC the voltage on the disconnect enclosure and on the shell of the water heater can rise to 120 volts. If you then touch it you could be injured or killed.

To correct this dangerous condition you can take one of two approaches.

One is to extend the feeder to the shed back to the main panel. Do you have two adjacent breaker slots available in the main panel? If you do you can run a three wire plus ground circuit from the panel to a junction box located near your water heater disconnect. You then splice the feeder to the shop into this new circuit at the junction box. The new circuit's EGC and grounded conductor (neutral) are connected to the bonded buss bar in the main panel. [this presumes that your main panel's cabinet is your service disconnecting means enclosure.] The bonded buss in the service disconnecting means enclosure is the only place that the grounded current carrying conductors (neutrals) and the EGCs are connected to each other.

The other approach would be to run a set of larger wires from your main panel to the location of your water heater's enclosed breaker. You would then replace the water heaters disconnect with a small panel assembly. This new panel would need to have at least four spaces but you could have more. You would then move the branch circuit for the water heater and the feeder to the shop into that new panel. In the new panel you would install a separate equipment grounding buss bar that fastens directly to the cabinet of the panel and is thus bonded to it. You would remove the green screw or strap that bonds that panels insulated buss bar to the panels enclosing cabinet. The EGC would connect to the bonded buss bar. The grounded current carrying conductors (neutrals) would connect to the insulated buss bar. In the main panel you would connect the two ungrounded conductors to the terminals of a two pole breaker that is sized for the wires to your new panel. The bare or green EGC and the white grounded current carrying conductor (neutral) would be connected to the bonded buss bar in the main panel just as in option one. The minimum sizing of that feeder would be fifty amperes.
--
Tom of the sparks and arcs

"This alternating current thing is just a fad. It is much too dangerous for
general use." Thomas Alva Edison

 

Did you put down a million $ security deposit or are you severly insured?

As a near-future landlord, I am shocked at what I have been reading here that renters do. I thank you for the reality check.

 

Actually, Karen-Z,
The landlord did all of the bad wiring, and I'm trying to figure out a way to work within it. Thanks for the advice on the insurance.
Drew

 

Yikes. Well, it's good then that you're trying to straighten it out, eh? Let's hope s/he doesn't hold you liable or blame you for the entire mess.

I had to laugh, though, when I read somewhere here that one landlord who was living in a duplex and renting out the other side had hooked up the renter's breaker box to the shared lighting and washing machine. He probably had his welder & hottub wired in there too.