Powering 5HP motor

[Ed Gibbons]

I’ll be using a double pole 30 amp breaker and running 10 gauge wire. Any problems if the run from the electrical panel to the outlet is 65’?

[Malcolm McLeod]

https://www.calculator.net/voltage-drop-calculator.html

Assuming a typical 20.5FLA on 5hp, this says you get a 2.6V (1.1%) drop at the end of the wire. Which means your amperage goes up by 1.1%, because the motor draws "Power". And P=iV, so for a given P, if V drops, then i increases.

Or in other words, you'll be fine.

[Rollie Meyers]

I’ll be using a double pole 30 amp breaker and running 10 gauge wire. Any problems if the run from the electrical panel to the outlet is 65’?

If using NM "Romex®" cable, 10 AWG is inadequate, to size the circuit the use of NEC table 430.248 is required, which states that a 5 HP motor is 28A @230V, 125% of that is 35A, so either 10 AWG THHN which is rated for 35A in this application or 8 AWG NM cable because NM sized in the 60 degree C column of Table 310.15(B)(16).

[Jim Becker]

Rollie, shouldn't he use the actual amperage rating for the motor rather than the "horsepower" for sizing this?

[Malcolm McLeod]

Rollie, shouldn't he use the actual amperage rating for the motor rather than the "horsepower" for sizing this?

I believe Rollie is correct on all counts.

I made 2 rapid assumptions that are contrary to 'general' use: 1) I have 1ea 5hp, 240v, 1ph motor in use - - and it's tagged 20.5FLA. So I just jumped on that, rather than look up the NEC std.; 2) I just finished wiring my shop with 10Ga THHN for all my 240V loads - - why would anyone use anything but THHN?!!? Oh, uhhmm, wait .... residential std IS probably NM?

[Ed Gibbons]

So I should use 8 gauge?

[Van Huskey]

Rollie, shouldn't he use the actual amperage rating for the motor rather than the "horsepower" for sizing this?

That is covered by pesky 430.6. There are exceptions for high pole count motors and multispeed motors but "our" 2 and 4 pole motors fall into the shown table.

Please correct me if I am wrong but doesn't article 430 apply only to permanently hardwired motors?

[Malcolm McLeod]

So I should use 8 gauge?

Or 10Ga THHN (stranded).

[Rollie Meyers]

So I should use 8 gauge?

If using non metallic sheathed cable "Romex®", yes.

[John K Jordan]

So I should use 8 gauge?

I erred on the side of bigger wire for mine, wasn't too much more money, just more work to make the connections in the boxes.

[Josko Catipovic]

I got a 6 HP Craftsman shop vac; runs fine on 14 ga extension cord.

[John K Jordan]

I got a 6 HP Craftsman shop vac; runs fine on 14 ga extension cord.

A 115volt extionsion cord, I'm guessing, if it's like my "6hp" Craftsman.

The thing about shop vacs, Craftsman and otherwise, is much documented - they lie, plain and simple, listing questionable "peak hp" numbers. The hp given is massaged and fudged under the umbrella of Advertising, likely because advertising honest specs couldn't compete with the rest of the pack. To get an idea of the true hp, find the full load motor amperage of the motor (if they list it) and look up the corresponding hp in a table. Sometimes they don't list it but it can be measured.

Look at what ShopVac has been forced to say about this:

"**"Peak Horsepower" (PHP) is a term used in the wet-dry vacuum industry for consumer comparison purposes. It does not denote the operational horsepower of a wet-dry vacuum but rather the horsepower output of a motor, including the motor’s inertial contribution, achieved in laboratory testing. In actual use, Shop-Vac motors do not operate at the peak horsepower shown."

If I plugged my 5-hp dust collector or air compressor into a 14ga extension cord I suspect it would melt.

JKJ

[Mike Henderson]

I got a 6 HP Craftsman shop vac; runs fine on 14 ga extension cord.

If you want to estimate the real horsepower, take the voltage times the current and divide by about 750. You'll get an estimate that will be a bit high but more realistic than the "6HP".

So, if you have a shop vac that says it draws 10 amps at 120 volts, that would be 1200"watts". If you divide that by 750, you get 1.6HP and that's a optimistic estimate.

Mike

[A HP is about 746 watts, but motors aren't 100% efficient so when you divide by 750 you're essentially ignoring the efficiency factor of the motor, which gives you a high value for the HP.]

[Van Huskey]

Please correct me if I am wrong but doesn't article 430 apply only to permanently hardwired motors?

Anyone know if the above is actually accurate? I thought/think that outside of a hardwired motor the manufacturer's suggested breaker is fine or in lieu of that a breaker and wire that is capable of carrying the motors FLA if it is indeed plugged in vs hardwired.

[Frank Pratt]

If you want to estimate the real horsepower, take the voltage times the current and divide by about 750. You'll get an estimate that will be a bit high but more realistic than the "6HP".

So, if you have a shop vac that says it draws 10 amps at 120 volts, that would be 1200"watts". If you divide that by 750, you get 1.6HP and that's a optimistic estimate.



Mike

[A HP is about 746 watts, but motors aren't 100% efficient so when you divide by 750 you're essentially ignoring the efficiency factor of the motor, which gives you a high value for the HP.]

A small induction motor like in a table saw or other hobby shop machine is in the 85% efficiency range, but a universal motor used in a shop vac, router, jobsite table saw etc is way less than that, 30% - 50%. So that 6 HP vac is probably more like .8 HP