Ground showing voltage?

Re: Ground showing voltage?

It depends on the meter... Some meters when on AC will read zero volts (or current) when measuring DC... Other meters will read a voltage (or current) when set to AC...

True RMS meters will read AC or DC voltage when set to AC (root mean square). "simple/cheaper" meters will not read any DC voltage on AC scale or something other than the correct DC voltage (i.e., they do not do the RMS measurements/calculations).

Take your meter, set to 20 VAC full scale and read your 12 VDC battery bank (assuming the battery reads 12.7 on VDC scale) and see what it reads (~0, 12.7 volts, or something different).

-Bill

And, if the light "shorts" out the voltage, then it is "safe" to connect the two grounds together (and usually a good idea to connect battery return to safety/frame ground).

Re: Ground showing voltage?

A 2,600 watt 120 VAC inverter will output ~22 amps--So you need breakers/fuses on 14 AWG and 12 AWG circuits to ensure that the wiring does not overheat if something gets shorted.

IF you DC ground your battery bank to a ground rod (and any major metal in the cabin like metal water pipes/etc.). Then you should use two pole ganged breakers (double pole breakers) and wire your 120 VAC circuits like they were two wire 240 VAC circuits.

This is because with a MSW inverter both 120 VAC leads are "hot" with respect to ground. You want both leads "breakered" and you want both to turn off (ganged) if one or the other "hot lead" shorts to ground.

If you have no "grounded metal" inside the cabin (i.e., plastic sink/PVC water/waste piping/etc.)--Then, in theory, you only need one breaker per branch circuit--because there is no way to "short to earth" one of the hot wires. You only have to protect against a short circuit (hot to hot short--i.e., a shorted AC appliance).

I hope I am being clear here--This is tough to describe in words and not be confusing.

-Bill

Re: Ground showing voltage?

Not trying to pick and argument with Chris (I probably would lose)... But grounding can get pretty complex and depending on lots of factors (brand/model/type of inverter) where grounds are made (ground rod, AC Neutral to Green wire vs floating), single vs double pole breakers (or two fuses--less good), what you are trying to protect against (a "floating" electrical system cannot cause a shock to ground--with the first connection--problem is the "second connection". The first connection creates a ground reference which is not usually detected, and then the second connection causes the current flow.).

Also, the amount of current--Under 8 amps of available current is usually fairly safe if you are using 14 AWG or larger wiring (i.e., you cannot overheat the wire unless you are >15-20 amps, for example). However, for electric shock, we are worried about leakage currents on the order of 0.005 amps (5 milli-amps) which almost any slight short (wet wiring connection, a bit of salt fog, etc.) can cause to flow.

So--While a floating power system is technically "safe" from ground faults--Because nobody goes around once a shift testing their floating/isolated power system--A "simple" current leak/fault will be hidden until the next time somebody touches a wet drill while standing in wet grass.

And--Ground Neutrals (DC Return bus, etc.) -- This is what allows us to use only one pole breakers/fuses... Because, there is never enough voltage on a grounded neutral (you may see a few volts) to cause enough current to flow and burn out a faulted neutral connection. And the Fused/Breaker'ed Black/Red Hot wire limits the outgoing current from the power source, so the neutral will never carry more current than it is designed for--Assuming standardize wiring practices are followed and there are not multi-point connections (paralleling of Neutral/Green ground wire, etc.).

MSW Inverters, since they are essentially split phase 120 VAC output--Have two hots and should use two pole/ganged breakers for protecting the "two hot" wires in the circuit... If one wire faults (hot to hot OR hot to ground), then the one breaker will trip and also trip its mate in the circuit--Helping safety because you "know" that both wires are killed in a short circuit (as always, never assume, measure/confirm/kill power before doing any work). (and add that the MSW wave form has its own issues with GFI breakers/outlets and AC loads designed for sine wave power).

Add grid power, different size generators, rocky/dry soil, lightning, etc... And you have a semester or two college electrical engineering course.

Because of the complexity--That is why I like to know about your installation, needs, and expectations--Throwing everything out there at once is confusing and usually counterproductive to a "simple" ground showing voltage? question.

-Bill

Re: Ground showing voltage?

Yes--That would be the "optimum" solution with a MSW (or floating TSW) inverter.

Regarding "colors"--You probably would want to use non-white wire for the circuit... (Or use colored tape at the junction boxes). White and Green (green/yellow are reserved colors and could confuse those following you later).

-Bill