De-rate on outlet

Futbalfantic

Well-Known Member
Joined
Aug 5, 2006
Location
Charlotte
In my garage I have a 60 amp circuit with a 50 amp outlet for the welder. (I'm pretty sure this is allowed by NEC due to the duty cycle of the machine). What I want to do is plug in a pressure washer with 20 amp draw on it and use an extension cord.

Is this allowed? Is there a way to add a fuse or breaker somewhere between the plug and the extension cord so if something happens to the cord it doesn't take 60 amps to trip the main breaker?
 
rockcity said:
This is a good comment. I assumed the pressure washer was the same voltage. If pressure washer isn’t the same voltage as the outlet, then no it won’t work.
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It will work great for a very brief moment :D
 
Also if the washer is really rated at 20A, be sure to get a real, quality extension cord also rated at 20A. Most of them are rated only 15 or 18A.

Of course thats w/ typical 110 cords.... given that it must be a 220 device, as per above... a properly matching cord is likely 10g or heavier and should be plenty rated....
 
Wait...electric pressure washer?
 
huh..never seen such a beast. Carry on.
 
Ron said:
Wait...electric pressure washer?
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I have a little 110v one. Only does like 1500 PSI, was like $80, good for washing cars and simple deck cleaning etc.
 
It’s currently a gas pressure washer but I have a spare 5HP 220v motor that I want to swap in. Just wasn’t sure about the extension cord.
 
a_kelley said:
rpms will be right. Gas engines are designed to run at 3600rpm... Most electric motors are designed to run at 3600rpm... What's the issue?
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Most electric motors are 1760 rpm in my experience.
 
I see both and more. 1740, 900, 1800, 3600 and multi speed.
We also have am 1800 rpm pressure washer.

Did @Futbalfantic verify the motor rpm against his pressure washer pump? Thats a good point
 
It's a 5hp electric motor, so a pulley system will give you whatever RPM you need. Should be plenty of power for a water squisher.
 
Its an analog device.
Technically you could make the new RPMs whatever you want, it doesn't have to match the old. It just depends what kind of pressure you want out of it.
As @jeepinmatt pointed out, you can easily change it w/ a pulley.
 
awheelterd said:
Most electric motors are 1760 rpm in my experience.
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Nah, if you're talking about 5hp compressor-style motors, 3500 and 1750 are common. The better/nicer ones are slower, the cheaper ones are faster.
 
Ron said:
I see both and more. 1740, 900, 1800, 3600 and multi speed.
We also have am 1800 rpm pressure washer.

Did @Futbalfantic verify the motor rpm against his pressure washer pump? Thats a good point
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That's what I was saying. If his pump was running at 1760 on the gas engine via a pull and he slaps a 3600 rpm electric on there without regearing, something is going to smoke.

Agreeing with @Ron you can't just assume a motors rpm. 90% of the motors that I have are 1760 (or 1750 wtf ever, they all say something a little different), with a smattering of 3600 rpm ones mixed in.
 
jeepinmatt said:
It's a 5hp electric motor, so a pulley system will give you whatever RPM you need. Should be plenty of power for a water squisher.
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Assuming it isn't shaft to pump input....
 
shawn said:
Nah, if you're talking about 5hp compressor-style motors, 3500 and 1750 are common. The better/nicer ones are slower, the cheaper ones are faster.
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This is wrong on so many levels, speed of the motor has nothing to do with quality. You can get shit motors that are base 1800 (usually includes all 1700-1900 RPM motors) RPM or 3600 (also a range from 3300-3600 RPM, 3450 is what I commonly see) RPM base or good quality units.
 
Ron said:
Assuming it isn't shaft to pump input....
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Yeah almost guaranteed this is how he was planning on doing it, hopefully using a Lovejoy or some sort of isolator. Assuming it's a cat or comet or other decent pump it should be easy to find the rated rpm, like said it's either going to be 1750 or 3500. Then look at the name plate rating on the motor, and knowing the universe you wont have the right combo. At that point you'd be better off buying a $90 predator from hf.
 
It's all about number of poles, etc., for an AC motor. A 2 pole works out to be 3600 RPM, and a 4 pole at 1800 RPM, but those are nominal speeds and not actual speeds. They may be rated at slightly lower RPM if they rate at load, which will be lower at rated torque from induction slip. You can't really have torque at the synchronous RPM, so it's more truthful to rate at the 1750 or wherever the rated load is instead of the nominal 1800.
 
No I have not looked at the motor RPM nor have I looked at the Pump RPMs.

Not going to be able to do a pump to motor mounting set up. If I use this motor I am going to have to build some form a shroud to go around the motor to prevent water incursion.

@shawn mentioned compressor style motors. His statement holds up. Cheaper compressors and their motors run faster. More expensive run slower.
 
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