Couple of questions on RPC build

I am going to be building my first RPC soon, and I have a stupid question. I have a 3 pole fuse block for power to go through on the way out to the machines. If the equipment motor is ten amps, do I use 3 ten amps fuses, or does the ten amps get divided between the 3 lines?

Also, I bought a lot of used electrical boxes at auction, and one of them had some volt meters on it. Would there be any benefit to wiring these in to see real time volt readings while the equipment is in use?View attachment 278950

If you believe NEC Table 430.52, you need 175% of the FLA with time-delay fuses or 300% of the FLA with non-delay fuses, or for a 10A 3 phase motor, either (17.5A) 20A, or 30A. Start-up current for small AC motors is 6X FLA, and that is unloaded. 10A fuses are likely to blow. You do not say what your voltage is, but the meters shown appear to be 500 V full scale and you probably would not be able to tease out important differences between the 3 phases. Current would probably be the more useful parameter to monitor. However, if you are going for the Mr. Carlson's Lab look, it does look slick. The conductor to the motor should be 125% of the motor FLA, or 12.5 A, so you could use 14AWG.
 
The conductor to the motor should be 125% of the motor FLA, or 12.5 A, so you could use 14AWG.
Technically you may be correct. However, I am pretty sure the NEC requires minimum #12 AWG for any motor over ¼ hp.
 
Technically you may be correct. However, I am pretty sure the NEC requires minimum #12 AWG for any motor over ¼ hp.

Since I'm invoking the NEC, then it appears prudent to continue in that fashion and go with the 12 AWG if that is what they say. I have no heartburn with that and 12 AWG and would prefer that to 14 AWG in any case. Thanks
 
I hadn't looked at the meters much before I posted, but you are right, they won't work with my application. The lights are also for 480, so I won't be using those either
 
Hi Barncat,

I'm curious ! Why wont the meters work for you, or the lights for that matter ?
 
The scale on the meters was pretty large, and inside of the box they were hooked to some sort of multipliers. I don't have the know how on how to get them to work for me. I put power to the lights to test them, and they didn't come on, either the bulbs we're burned out, or they actually need something closer to 480 as the sticker on them says.
 
Hi Barncat,

You could always test incandescent bulbs with a cheap multimeter, though many indicator lamps like that are actually neon bulbs with a series resistor.

As far as the meters are concerned a close up picture of the front and any wiring at the back would help Identify exactly what they are, because they would supply useful information as to how well your RPC was functioning.
 
Technically you may be correct. However, I am pretty sure the NEC requires minimum #12 AWG for any motor over ¼ hp.

Just had a few minutes to check. 2017 NEC Article 240.4 (D) permits 14 AWG, so 14 AWG is correct. Also, 430.22 (G) explicitly permits 14 AWG. Do you have another cite in the NEC that says something else?
 
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The scale on the meters was pretty large, and inside of the box they were hooked to some sort of multipliers. I don't have the know how on how to get them to work for me. I put power to the lights to test them, and they didn't come on, either the bulbs we're burned out, or they actually need something closer to 480 as the sticker on them says.

The things you identify as a multiplier is likely a voltage divider generally comprised of resistors. You can use the existing meters if you know the resistance of the meters, current is usually given at full scale and labeled on the meter, in which case all you need to do is build a new divider network, however, your meter scale at full deflection is labeled "500" I have seen folks write their own scale and past over the old scale, and adjust the divider network accordingly. But they always look a bit cheesy, and new meters are relatively cheap. Frankly, I would scrap the meters or give to someone who can use them, and proceed building your RPC without them.
 
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