Electric wiring help please

[cubicdissection]

My shop is the back half of an old warehouse / industrial building downtown. The electric is a hodgepodge of new and old. Right now all my tools run off three 30A circuits; two older with screw in fuses, and one newer with a breaker in a box thats maybe 10 years old.

I'm looking to run a 220 line back to run my new milling machine. The new box on the left of the pictures is already setup for fuses for a 220 line, but the outlet is right next to the box. I need it in the back of the warehouse.

I went to lowes and priced out 1/2" flex conduit and single strand wire to run it back. The run will be about 160 feet total for the new outlet.

My question is, if I'm going to make that run for just one outlet, why not put in a sub-panel back there so I can drop more lines later if I need them? One of the fuses in the newer box with the sharpie marks is 50 amps; it was for an electric kiln that's no longer being used. Can I run that 50A on heavier wire right from the existing box to a smaller subpanel, and branch off for the new 30A 220 line from there, or is that against the rules?

Here's a couple pics of the existing electrics in the bldg...if you click on the links below each picture it will link to higher resolution pics. TYIA!!!

http://www.cubicdissection.com/temp/elec2l

http://www.cubicdissection.com/temp/elec1l

 

[Woodman2k]

Eric,
I don't have my hand book handy but on a 50 amp circuit that has a run of 160 feet you would need to use at least 8 gauge and better would be 6 gauge wire to limit the voltage drop over that long of a run.It's legal and definitely better practice to make that run with a subbox and I will check on Monday to verify wire size but 1/2" conduit will not be big enough.You will have to use copper wire also.PM me if you have any other questions. Greg

 

[cubicdissection]

Thanks Greg, I sent a PM.

 

[steviegwood]

It looks like you have plenty of room in the panel on the left that you could drop a higher amp breaker in if you want or replace the fifty. If I were setting a new sub panel in the back of the shop and wanting more circuits I would consider running a 100amp service to the back. You then could make that run with 100amp aluminum wire for close to the same cost if not cheaper than running copper that far. You still would not have the current drop. Come out of your sub panel to your outlets with proper sized copper wire though. Someone can jump in and correct me if I am wrong. You also may want to check any local codes on that because I am not familiar with your area. You may want to check your local codes on grounding the sub panel that you set also. Steve

 

[scsmith42]

For a 160' run, 240 volts, in order to keep the voltage drop below 2%, here are the maximum amps per copper wire size:

20A - requires #8 wire
30A - requires #6 wire
40A - requires #4 wire
50A - requires # 4 also
70A - requires #2
100A - requires #1/0

As per my Pocket Reference

 

[cpowell]

The writing on the panel on the left (and the safety disconnect that feeds it) raises some questions for me.

Phs A - 120 Black
Phs B - 240 Red
Phs C - 120 Blue

Ph A, B, C usually refers to 3 phase power. Phs B = 240 does not make sense for a balanced 3 phase voltage source, whether the voltage is read Line-Line or Line-Neutral. Is Phs B a "stinger" leg? Notice that nothing on the panel is connected to "Phs B".

Can you open the disconnect box and get a shot of the wiring inside?

I wish you were close by so I could check this out for you. Do you have an electrician or EE friend that could check this out for you and also make certain that proper grounding is used?

Chuck

 

[cubicdissection]

Hi Chuck, thanks for your post! Most of what you said was greek to me, but I'll be heading to the shop in a bit. I'll pull the big lever (why is that so satisfying? Last time I did it I shouted "It's ALIVE!!!" ) and will post pics of inside of the panel and disconnect box as you requested.

Rest assured I won't be moving forward on this until I'm comfortable that I know what I'm doing! Hopefully with your guys help I can get to that point...if not I'll hire an electrician, maybe see if I can find someone on CL willing to stop by and do the final hookups after I do all the grunt work running the wires/conduit.

 

[cubicdissection]

Chuck, here's pics of the panels:

http://www.cubicdissection.com/temp/elec3l.jpg

http://www.cubicdissection.com/temp/elec4l.jpg

 

[Gotcha6]

The absence of any breakers on the 'B' phase in the panel leads me to believe you have what's called a 'high leg' service. This was used many years ago when 3 phase service wasn't available to an area to run compressor motors for A/C units, etc. The middle. or 'B' leg would indeed read 240 volts to ground - and should have been marked with ORANGE tape to identify it. This is a very complicated setup for a layman to tinker with. I'd call in an expert.

 

[cpowell]

The pics look like 3 phase power. I am not sure how it's derived though. Let me clarify.

If the power comes from a 4 wire delta system with a center tapped A-C neutral then the phase-to-neutral readings should be 120V (Va-n), 120V (Vc-n), 208 V (Vb-n). Line-line voltage should 240V (ie, Vab, Vbc, Vca).

Power from a 4 wire Y system with grounded neutral would have all line-neutral voltages at 120V and line-line voltage at 208V.

It doesn't look like ground wires were used a lot in your panels or field wiring.


Chuck

 

[cubicdissection]

Well, thats kind of discouraging. However, all I really started out to do was run a 220 line. No reason I can't tap into the existing 220 outlet, cover it with a block plate, and run wires/conduit from where it is currently to where I need it.

I won't be messing with any of the complicated stuff in the boxes in that case; just extending an existing run. I think the line is 20 amps on each wire, so that solid 10ga copper should do me for the length of the run right?

 

[Gotcha6]

It doesn't look like ground wires were used a lot in your panels or field wiring.

If the system was wired using MC cable, EMT, IMC, or Rigid metal conduit, grounding would have been achieved through the conduits themselves. That appears to be what you have. If you use any other type of branch circuit feeder you'll need a ground wire.

 

[scsmith42]

I think the line is 20 amps on each wire, so that solid 10ga copper should do me for the length of the run right?

Not if you want to keep your total voltage drop to less than 2%.

 

[cubicdissection]

Not if you want to keep your total voltage drop to less than 2%.

Hmm. I emailed the vendor asking about the amperage requirements for the machine. He replied that it only needs 8-10 amps at 220, so 15 would definitely do it. My plan is to tap into the current outlet box and simply extend the wires inside 1/2" flex conduit.

If one of you kind gentlemen could advise what gauge I need for a 142' long run at 15 amps, I think we can consider this issue closed

 

[ptt49er]

For a 160' run, 240 volts, in order to keep the voltage drop below 2%, here are the maximum amps per copper wire size:

20A - requires #8 wire
30A - requires #6 wire
40A - requires #4 wire
50A - requires # 4 also
70A - requires #2
100A - requires #1/0

As per my Pocket Reference

Scott posted this earlier, I think it answers your question.

 

[scsmith42]

According to my Pocket Reference, for a 15A load on 240VAC,

10 guage wire is sufficient for up to a 150' run.

The other question that you'll need to ask yourself is how much flexibility do you want to have with the wiring run that you install.

If you're only operating a single piece of 240V equipment, you may not require a neutral (check with the manufacturer). Thus, you could run a 10/2 with ground.

However, In the event that you want to tap a 120V circuit off of it at the end (half the available amps), or if your 240V equipment requires any 120 V (such as for an work lamp, etc) for wiring you'll need to run 10/3 with ground so that you'll have an extra neutral wire for the 120V.

Clear as mud?

You will also need to make sure that the outlet that you will be tapping off of is fed by 10ga wire or larger.