Wiring a 100amp outlet/connection- typical practice?

[tarbellb]

Im in the middle of a service line upgrade for my property and shop.

I will need a few high amp connections in the shop for certain tools (large 20hp VFD screw compressor, laser machine, welders, etc..)

What is considered best practice or typical for a 100amp and 60amp 1ph 240v connection
_ hardwired?
_ do i need or want a shutoff
_ anything else to consider


My setup will be using surface mount conduit, the run from box to panel is under 10ft

 

[u2slow]

Pin/sleeve is often used for these higher amp connections. I would hardwire though, as those get really pricey.

At 10' I'm content to use the breaker as the disconnect.

 

[tarbellb]

The panel/load center is on exterior, if that makes a difference @u2slow

 

[wyliesdiesels]

At 10' I'm content to use the breaker as the disconnect.

only allowed if the equipment is within site of the disconnect, which in the OP's case, is not

 

[wyliesdiesels]

compressor and I assume laser machine, are not portable, so i would hardwire those to a disco.

the welders, I assume, are portable and thus a plug and receptacle would be best

what is the make and model on the welder?

 

[wyliesdiesels]

The panel/load center is on exterior, if that makes a difference @u2slow

it does. see above comment #4

 

[u2slow]

only allowed if the equipment is within site of the disconnect, which in the OP's case, is not

I assumed it was within sight, since 10'.

OP has now clarified.

 

[matt_i]

Hardwired is cheapest but gives minimum flexibility in the layout as times change. 3 pole non-fused disconnects are still pretty cheap, in good-used condition, if you want to go that route.

A screw compressor or machine tool (etc) may have its own 3 pole disconnect native to the machine...

 

[mike93lx]

If all the equipment will be line of sight to a spot in the shop, a sub panel would likely be easiest.

How are you hooking up the 20hp vfd? That's not single phase, right?

 

[tarbellb]

If all the equipment will be line of sight to a spot in the shop, a sub panel would likely be easiest.

How are you hooking up the 20hp vfd? That's not single phase, right?

Yes it's a single phase compressor

Sub panel could be the move. I'm pulling 100amp feeder to the original sub panel. My thought was running a couple surface mount boxes would be easier but now a the shut offs requires it could be cheaper.

 

[mike93lx]

Yes it's a single phase compressor

Sub panel could be the move. I'm pulling 100amp feeder to the original sub panel. My thought was running a couple surface mount boxes would be easier but now a the shut offs requires it could be cheaper.

20hp on single phase service? Is this OK with your poco?

 

[alfredeneuman]

Any switching device between the VFD and the motor will, when under load, will do damage to the VFD's output transistors. This will greatly decrease the life of the VFD.
Make sure the equipment isn't running when you throw the switch (except in an emergency)

 

[Lassen Forge]

20hp on single phase service? Is this OK with your poco?

Had to look it up - 1ø 230 V, a 20 HP motor pulls 88 amps. If you got the service and the $$ for electricity, why not? Cheaper in the long run to go 3ø...

 

[mike93lx]

Had to look it up - 1ø 230 V, a 20 HP motor pulls 88 amps. If you got the service and the $$ for electricity, why not? Cheaper in the long run to go 3ø...

Because power companies will have limits as motors draw far more current at startup than running.

A normal residential transformer will not support a 20hp motor starting as it could be a few hundred amps

Limits are usually 5, 7.5 or 10hp on the high end for residential service

 

[wyliesdiesels]

Had to look it up - 1ø 230 V, a 20 HP motor pulls 88 amps.

where did you come up with 88a? the NEC FLC chart for single phase doesnt go past 10HP, which is 50a

regardless, the in-rush current would be 4-8x and a residential service would not support that kind of load starting on the line.

most PoCos also have HP limits for residential services and small commercial.... you will probably trip the main breaker starting that motor

 

[jar944]

regardless, the in-rush current would be 4-8x and a residential service would not support that kind of load starting on the line.

most PoCos also have HP limits for residential services and small commercial.... you will probably trip the main breaker starting that motor

Ideally op needs a 3ph motor and a soft start (vfd or otherwise) if they want 20hp on single phase power. Now that does assume the compressor would function with a soft start.

 

[jblnut]

As mentioned I’d absolutely check with the PoCo before wiring up a 20hp single phase motor. We asked about a 15hp single phase motor for a grain bin and they said “sure, as long as you sign this paper that says you’re responsible for any issues on the line up to the substation that we think you caused”. WTF yeah nope lol. So anything larger than 10hp here is 3ph and is either on a rotary phase converter or a VFD.

 

[jblnut]

Ideally op needs a 3ph motor and a soft start (vfd or otherwise) if they want 20hp on single phase power. Now that does assume the compressor would function with a soft start.

I have a 40hp well pump behind a rotary converter with no soft start that I know of unless the rotary converter has one built in but I don’t think it does. But the same dudes wouldn’t let me start a 15hp single phase motor for some reason lol.

Why wouldn’t a compressor work with a soft start ? The unloading valve should have the head at 0psi so it should fire up just fine even if it isn’t getting max amps/hz right away. My larger grain bin fan motors on VFD’s are using the VFD exclusively to ramp up to max speed. They start under a larger load right away than a compressor would I’d think.

It’s a distinct possibility I don’t understand how a soft start works and if so please disregard 🫣

 

[Lassen Forge]

where did you come up with 88a? the NEC FLC chart for single phase doesnt go past 10HP, which is 50a

regardless, the in-rush current would be 4-8x and a residential service would not support that kind of load starting on the line.

most PoCos also have HP limits for residential services and small commercial.... you will probably trip the main breaker starting that motor

It was some chart on an electrical supply site's catalog - contactor section....

https://www.sprecherschuh.com/content/dam/sprecher-schuh/ecatalog/hp-volts-fla_charts.pdf

Probably read it wrong - in a pinch I defer to those who actually KNOW this stuff.

 

[wyliesdiesels]

It was some chart on an electrical supply site's catalog - contactor section....

https://www.sprecherschuh.com/content/dam/sprecher-schuh/ecatalog/hp-volts-fla_charts.pdf

Probably read it wrong - in a pinch I defer to those who actually KNOW this stuff.

yeah those numbers are from the NEC FLC chart in 430.248.... they are NOT full load amp ratings which would come from the motor nameplate.... they are max ratings for motors with those HP ratings and it is what you size your wire off of....

and standard NEMA size motors stop at 10hp 1Ø.... farm duty go up to 15HP.... i could not find a 20HP 1Ø motor anywhere online to check nameplate rating...

 

[mike93lx]

yeah those numbers are from the NEC FLC chart in 430.248.... they are NOT full load amp ratings which would come from the motor nameplate.... they are max ratings for motors with those HP ratings and it is what you size your wire off of....

and standard NEMA size motors stop at 10hp 1Ø.... farm duty go up to 15HP.... i could not find a 20HP 1Ø motor anywhere online to check nameplate rating...

https://ebay.io/m/r1QeNx

 

[wyliesdiesels]

that in-rush rating is awfully low

my 3-ton AC condenser pulls almost 100a on startup and its not even 5hp

 

[Cruzan80]

that in-rush rating is awfully low

my 3-ton AC condenser pulls almost 100a on startup and its not even 5hp

Clicking the eBay link and reading the description, it looks like it is a 3ph motor with a static phase converter. Part of the motor says "Baldor", but all the labels look like homemade Avery Peel-n-stick is a big clue this isn't factory. Says "Seller Refurbished"

It is anyone's WAG how he got the inrush current number, along with the others as well, probably.

Quote from listing "This is a modified 3 phase motor. Comes in two parts, a control box and the motor. "

Not attacking Mike here, just this is not a "normal" or factory 20HP 1ph.

 

[wyliesdiesels]

aww well that makes sense

 

[tarbellb]

20hp 3ph running on soft start VFD

I have the spec sheet here somewhere, I'll try to post it.

 

[mm08822]

that in-rush rating is awfully low

my 3-ton AC condenser pulls almost 100a on startup and its not even 5hp

Code letter F indicates 5.0 - 5.59 KVA/HP for locked rotor. At 230vac, that is on the order of 434 - 486 A. It's also for across the line starting which is not the case here with the vfd. The vfd bus will provide a little buffering. Ramp rate (accel) could also be played with.

Somebody is going to notice this starting. Voltage sag could even be great enough to fault the drive. Needs a beefy service.

 

[Lassen Forge]

yeah those numbers are from the NEC FLC chart in 430.248.... they are NOT full load amp ratings which would come from the motor nameplate.... they are max ratings for motors with those HP ratings and it is what you size your wire off of....

and standard NEMA size motors stop at 10hp 1Ø.... farm duty go up to 15HP.... i could not find a 20HP 1Ø motor anywhere online to check nameplate rating...

Thanks, Wylie... I'm glad you shouted out, Electrics are nothing to F*** with, and really, you need the practical to have someone convert theoretical charts to real life.

 

[jar944]

Somebody is going to notice this starting. Voltage sag could even be great enough to fault the drive. Needs a beefy service.

Only if the start ramp is very short in duration.

 

[jar944]

I have a 40hp well pump behind a rotary converter with no soft start that I know of unless the rotary converter has one built in but I don’t think it does. But the same dudes wouldn’t let me start a 15hp single phase motor for some reason lol.

Why wouldn’t a compressor work with a soft start ? The unloading valve should have the head at 0psi so it should fire up just fine even if it isn’t getting max amps/hz right away. My larger grain bin fan motors on VFD’s are using the VFD exclusively to ramp up to max speed. They start under a larger load right away than a compressor would I’d think.

It’s a distinct possibility I don’t understand how a soft start works and if so please disregard 🫣

Is it a 80 or 100hp rpc? The rpc is acting like a buffer, but the inrush starting the rpc itself is significant.

 

[jblnut]

Is it a 80 or 100hp rpc? The rpc is acting like a buffer, but the inrush starting the rpc itself is significant.

100hp. It drives the well pump as well as all the drive motors on the pivot itself. It makes sense that the rpc is a buffer as it's sort of a giant flywheel when it's spinning.