My dad is using 220 v wiring but it's only outputting 110. He wants to isolate the problem instead of replacing the entire length of wire. Any idea what he can use to detect where the fault is occurring? I've looked but can't find anything.

I am assuming you have access to both ends of this cable, and there are no other junction boxes in between where a splice could have failed. I also assume the circuit breaker has been tested for proper output.

There is no instrument feasible for a DIY'er to find a break in a cable, of course this really depends on the size and length of this cable.

There are instruments available, as shown below, that we use to find open breaks in cables. We use the Greenlee, for about $500. I never heard of the other one for $150.00, but I bet it works the same. There may be others available, but none will be too cheap, unless you can find a used one on Ebay

Electricians use Greenlee products for many things, I don't know why, because that green paint is very expensive.

Power Probe PPECT2000 - Electronic Short/Open Circuit Tracer - SJs Tools

Greenlee Power Finder Open Circuit Tracer, Greenlee Textron, Circuit Tracer - Mfg# 2008

If there is some reason that replacing the cable makes it not feasible or practical, then a service call from a service electrician that has one of these units may be in order. Course, the break will need to be accessible to repair the cable.

Really depends on the size, length, and accessibility of the cable the best way to handle this.

You maybe making a mistake so basic tkrussel doesn't realize anybody would do it. You are measuring the voltage hot to hot? Each hot will only be 110 above neutral or ground. You have each hot connected to a separate pole of a double pole breaker? People have bought tandem breakers which give two 110 circuits off the same leg of the box. You need a double pole breaker which has 2 contacts one to connect to each leg.

I would think a broken wire or bad splice would give 0 volts. There is a DIY priced tool that can find broken wires in exposed romex. I came across the niftiest gadget for trouble shooting, a voltage detector. They work through the insulation of wires. There are several brands. I have a GB Instruments GVD-505A, less than $15 at Home Depot. Touch it to a hot wire, and the end glows red. Find the doodad that lights it on one side, and not the other, and you have the culprit. You do not have to open up housings and expose electrical contacts. You are looking at where your hand is, not where the meter is. Most people are capable of doing repairs and will get it going and not get hurt if they use a little sense. The voltage detector makes it even easier.

Thanks for both responses. I'll give them to Dad, whose having the problem. I do know that it used to run 220 so thinking it was rigged properly and hasn't been changed. But the wiring is pretty old (20+ yrs, I think). The cost involved is in replacing the entire length from the house to the dock which is about 500 ft and buried.

Thanks again for your advice!

I am betting the wire is fine, it is a connection at one end or the other.

If you have the situation that labman is saying you would get no voltage reading instead of 240 when you try to read hot wire to hot wire because there is no potential difference (both hots of the same leg, same as putting your test reads on the same energized wire.

To test this read hot to hot if you read no voltage . Read hot to ground for each hot wire if you get 120v on each one then you are wired as labman is saying. If you get it on only 1 side chances are you have a fault or even a side of a double pole breaker.