Because of voltage drop my customer is suppliyng me with 1/0 cable from MCC to my skid edge for a motor heater 120/1ph/60hz/5.5A. Planning on terminating 1/0 wire in a junction box on a Power Distribution block and stepping wire down to a #6AWG. My question is for wire cost what is the smallest wire i can use instead of #6AWG for 25' run from the jucrion box to the motor heater without affecting the voltage drop?
Voltage Drop from MCC
- Thread starter rene92
- Start date
- Status
- Occupation
- Licensed Electrician
The smallest allowed is 14AWG. What does it matter about voltage drop for an engine heater? The heater will get warm even if you 20% VD.
Fitzdrew516
Senior Member
- Location
- Cincinnati, OH
Exactly what I was thinking. Purely resistive loads make this one easy.
Fitzdrew516
Senior Member
- Location
- Cincinnati, OH
Also... these numbers weren't making sense to me so I checked them. What percentage of VD are you wanting? Theoretically speaking even at a MILE (which would never be done lol) the VD on a 120V circuit with 5.5A and 1/0 CU conductors would only be about 5.9% on a resistive load. You can go 500' with #6's and only be at 2.25%. Something isn't adding up here.
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
Not only that, but for the cost of that 1/0 wire, why wouldn't you run a pair of 14ga wires at 480V out to a box next to the motor and put in a little 750VA transformer (assuming you can't change the heater voltage)?
VOLTAGE DROP
VOLTAGE DROP
I gave the wrong info. It's not a motor heater but a 525w Frame Space Heater but am still trying to use smallest wire possible out of my junction box and staying within a 5%VD. Will changing to a substantially smaller wire size at the junction box have any affect on the VD at such a shotr distance?
VOLTAGE DROP
I gave the wrong info. It's not a motor heater but a 525w Frame Space Heater but am still trying to use smallest wire possible out of my junction box and staying within a 5%VD. Will changing to a substantially smaller wire size at the junction box have any affect on the VD at such a shotr distance?
Fitzdrew516
Senior Member
- Location
- Cincinnati, OH
How far away is the heater?
25ft
Fitzdrew516
Senior Member
- Location
- Cincinnati, OH
525W with a 25' run @ 120V would be .36% VD with #12 CU conductors... I'm confused as to what the issue is.
no issue
just wanted to make sure i wasnt going to affect the voltage changing to such a smaller wire size copmared to 1/0
Fitzdrew516
Senior Member
- Location
- Cincinnati, OH
Got it. Yeah, I'm not sure why anyone would think you would ever need 1/0's on a 120V, 525w load. You could go a little bit over 200' and still stay under 3% VD on that branch.
Are you absolutely sure you got all the numbers right (voltage/phase/wattage/etc.)? I'm only asking because I find it curious where the idea for the supplied 1/0's came from.
Just to maybe put this into perspective - Your standard residential portable space heater is typically about three times the load you've given us.
Yes all correct, the customers MCC in the plant is a good distance from the motor skid since were operating in a hazardous area not exactly sure how far it is just that I need to provide for their 1/0 wire.
luckylerado
Senior Member
- Location
- Lake of the Ozarks
Ignoring feeders and assuming appropriate OCP is provided and copper conductors are used:
If you can keep the 1/0 portion to below 2835', your smallest wire would be a #18.
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
I agree with augie47, something is amiss here. 10ga instead of 1/0 sounds like a lot more possible scenario.
I can't imagine that connecting 1/0 cable to a little 525W heater is going to be even REMOTELY possible!
I can't imagine that connecting 1/0 cable to a little 525W heater is going to be even REMOTELY possible!
Operating in a harzardous area?
a 120/1 20 A ckt from an MCC?
gotta be a closer source of power
what is motor skid?
and a frame heater?
If all this information you've given is actually true and accurate then your customer is grossly misinformed and you're enabling their ineptitude. This is a good example of when you shouldn't let a customer tell you how to do your job.
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