house wiring voltage drop

That voltage drop is excessive. The National Electric Code specifies a drop of no more than 5% from the breaker box to the furthest outlet at full load (Note that a 1500 watt load is about 85% of full load).

Checking the drop at various points from the breaker box to the outlet supplying the computer is a good idea. The faq at

PlainBill

Hi PlainBill,

Thanks for the response and the link. I will go back to my friends and look for the problem. I suspect there is a loose connection at one end or the other since it seems to be intermittent. Checked my own wiring with same load and only had a 4 volt drop.

billfre

Your own experience is more typical. 10 V is excessive. Aluminum wiring??? I would be careful not to keep the load on continuously just in case there is some heating somewhere in the walls. P = IV =

With standard wiring practices there are several outlets in this run of wire. The most likely point for a problem is at the point an outlet or switch is connected to the wire. IF you can determine intermediate points along the wire run, the best approach is to determine if the majority of the drop occurs between a pair of outlets.

Someone else gave a wattage - they miscalulated. The TOTAL power dissipation for the drop is about 125 watts - still a sizeable amount. The EXTRA dissipation is about 75 watts. One approach would be to hook up the 1500 watt load, then carefully check outlets to see if any feel warm. If no suspects are identified, wait 15 minutes or so (with the load still present), then repeat.

PlainBill

Billfre-

Also look for evidence of a poor neutral connection. When that happens, voltage will divide according to the load on each line. If that were the case, ten volts drop at a high current load could cause a ten volt rise across the other line-to-neutral circuit.

Five or ten volts doesn't sound like a serious problem, but a poor neutral connection could get worse with age.

Fred

Fred,

Thanks for that tip, I think it may be the problem here. I went back and tightened the screws on both leads at the outlet and at the hot side on the breaker. One screw at the outlet tightened maybe a quarter turn. This brought the voltage drop down from 10v to 7v. Still over the 5% specified by code. I also put a voltmeter on another outlet in the same room that was on a different breaker. When I loaded the outlet that had the 7v drop, the voltage at the other outlet went up a couple of volts from 120v to 122v and I wondered, what could cause that?

Then you posted about the poor neutral and I thought about the 2v rise I had measured at an adjacent circuit. Then remembered that I did not check tightness of the neutral wire connection in the panel. Think I will go back again and make sure the neutral wire is good and tight at the panelboard. Maybe that is why it is still over the 5% drop spec.

Does this make sense?

Measure the drop at the breaker too.

My experience with an open or loose neutral wire, is that the problem is usually outside of house. The problem is usually with the electric company's wiring. Call the electric company. They usually don't charge to check their equipment.

The problem is only at one wall outlet inside the house. Please explain how it could be caused by a problem outside the house. .

Bilfre-

This problem exists somewhere between a power company transformer and where the neutral connects in your breaker box.

When I had the problem, I called the power company. Their man checked the transformer, but said I would have to hire an electrician to fix my end of the circuit. While he had the meter removed, he went ahead and tightened the connection there, which solved my problem.

Fred