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Electrical Question
- Thread starter slash007
- Start date
I am an electrician by trade. Code requires a 12 gauge wire for a 5 hp 3 phase motor. I know of no benefit to using 10 gauge wire. (.63 versus .40 voltage drop that's 23 one hundredths of a volt less voltage drop for 10 gauge at 20 feet in length.) Code permits up to a 30 amp breaker but does not require it. (30 amp is allowed on 12 gauge wire for a motor load). I have 5 bays running on 20 amp breakers with 5 hp motors and 1200 psi. I don't remember the tip size but the motors pull about 8-9 amps. You are only using about 2.6 hp of the 5 hp motor anyway. Could have kept your old motors and saved a bit but oh well. gpm x psi then divide by 1460 for how many hp you need. Lots of misconceptions out there. As pointed out above 3 and 5 hp motors turn at the same speed and therefore pump the same amount of water. Buy a 500 foot roll of 12 gauge thhn wire at lowe's and tape the wires black red blue left to right and top to bottom. Run a fourth black wire and tape it green for grounding. (If you want to be technically right you need to buy a roll of green wire because you are not permitted to reidentify smaller than 6 gauge wire but it's the exact same product with a different color jacket so I would have a hard time spending another $50 for green instead of $2 for a roll of green tape.)
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Thanks for the tips. I didn't buy new 5hp motors as they were already on the used pump stand I bought and refurbished. Good tip on the green wire, I did that a lot when I ran new wires for my vacs. Bought red, green and white tape and just used the black wire.
mjwalsh
6 bay SS w/laundromat
Based on wash4me's above quote ... that (gpm x psi)/1460 is the limiting factor & it still does not tell us what the amps the specific motor draws when it first starts up. It seems like single phase is worse when it comes to the starting amp criteria creating the need to go to a higher amp breaker. As far as the breaker throwing ... I have read that some breakers & even between brands do not all have the same throw sensitivity. Older Federal breakers come to mind. Our friend Slash007 could be considering a Super Bay(s) with more pressure & volume if the pump part of the equation can handle it.
mike
Should I use stranded or solid wire for the pumps? Also, I have been going back and forth between using 10 and 12 gauge wire after your post. My cable run is only going to be 25' or less, so it seems that I can get away with a lower gauge wire.. Other than that, is there a limit to how many wires I can run in the conduit? I am going to have 26-28 wires total.
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MEP001
Well-known member
I already told you the inrush current on the motor when it starts: it's not measurable. There's not a 5 or 10 second spin-up time on the motor. It's also not single-phase, so your comment there is off-topic rambling.
MEP001
Well-known member
Stranded wire is used for flexibility. Either one will do the job the same.
Here's a chart for number of wires in a conduit:
https://www.theautomationstore.com/maximum-number-of-conductors-in-conduit/
MEP is right. stranded or solid is just a preference. Stranded is my preference. What about possibly using the wire out of the old pump stand? You won't know the difference between 8 10 12 14 gauge. It's irrelevant other than code requires at least 12 gauge. When you put a lot of wires in a conduit it is technically a code violation if you don't "derate each conductor". There's a procedure for this but it's really not going to hurt to run them all in a conduit and not worry about it. Carwash pumps don't run continuously and are lightly loaded. If you were going to run fans that were fully loading each motor and running all day continuously then you should derate. If you're worried about this derating it would be code compliant to run a separate conduit for each 2 pumps and then share the ground between the 2 that are run together in each conduit.
Starting inrush is 5-7 x full load amps listed on the motor but it only lasts like 1/10 of a second or something. It is already taken into account with the code recommended size of 12 gauge wire. Different breakers have different trip curves but that is just fine on a 20 amp breaker of any brand. No harm in putting in 30 amp it's just I'd rather have the money. Single phase does require more amps to run and start because it's just 2 wires instead of 3 putting power to the motor. We put in a truck bay with a bigger pump but the same 5 hp motor. It put out 5 gpm at 1250 psi and It would occasionally trip the breaker so we turned the pressure down a bit. Could have put in larger breaker i suppose.
Thanks! I searched for something like that, but couldn't find it. I was worried about putting in too many wires in one conduit. I plan on using the flexible grey conduit, probably 3/4 inch. Looks like with THHN at 12 gauge, i can fit 18 wires, so maybe I'll just use two runs and put 14 in each if they fit.
wash4me, the wires used in my old stand won't work because they are too short and run way differently. It is a custom stand and the power runs to a box on the wall from the breakers, then splits out to each pump. It is also almost 40 years old, so replacing it is the way to go. I guess if I am going to stick with 20 amp breakers, then might as well use 12gauge as well.
Thanks.
Use the metallic sealtite and you won't want that many wires in it. It is possible but a pain. 3-4 runs of conduit. It's important to keep all 3 conductors that go to a motor in the same conduit.
Sam, Good luck pulling 18 wires through that. In my 7 bay stand I ran a 1 1/2" PVC conduit About 25' To a 12" Steel pull box. From there a 1 1/2" Liquidtight conduit to bottom of the UCC Cabinet. The last few pulls on that were tough. If you can pull all your wires at same time you will get more wire in each conduit. Get a few bottles of easy pull lube!!!
Currently all the wires were run using a 1 1/2" liquidtight conduit and all wires fit in there. It was setup for a 7 bay and an auto and I only have 6, so at least 5 less wires have to fit in there. I couldn't find 1 1/2" liquidtight at Lowe's or HD. Where did you get yours? At least I only have to run liquidtight for about 12'. The stand is very close to the breaker and pull box.