20A 240V plug/receptacle choices, and running 5HP <20A motors on 12AWG circiuits?

[Dave MacArthur]

Hi all. I've recently purchased some 240V machines with 3-5HP motors. All came wired with locking plugs on them, 3 poles and ground (4 prongs), 20A plugs of type L1420P. Don't know why 3 poles, motors all require only 2 plus ground on these, I'd have expected L6-20P...

My shop and machines are currently wired with non-locking 6-20P.


Both are fine according to NEMA charts (here's a nice reference from previous thread at SMC asking about 240 v plugs: http://www.powercabling.com/nema.htm )

Question 1: Thoughts on using straight bladed plugs instead of locking ones currently on the machines, which would let me use my currently installed receptacles? Just personal preference it seems, but anyone have any supporting stories?


Question 2: Can I replace these locking plugs on the 5HP machines and run them on 20A circuits, 12 gauge wiring with 20A CB to a subpanel I installed myself, without issues? Previously I just assumed that a 5HP motor would need a 30A circuit on 10AWG wiring, but now looking at the motor plates and seeing them all rated less than 20A, I'm thinking my 20A circuits are OK? Garage shop, hobby use. As I read the NEC, 12AWG can do 25A, over-current protection to be 20A. So I'm thinking if the machines don't trip the 20A, should be good?

Here's the machines, motor ratings and motor faceplate or instruction manual amperage:

SawStop ICS 5HP 19.7A from both motor plate and manual. Manual says saw should be wired with a 3 wire (hot/hot/ground) and NOT a 4 wire plug/cable, tells you to cap the neutral if you have 4 wires run.

Oneida 5HP cyclone DC, 5HP Baldor, 19.5A, good at 20A if my CB can handle the start up (slow trip one). Also shows only 2 wires and ground on their motor wiring diagram.

Anyone out there running these or other "5HP" motors rated just less than 20A on 20A circuits and have any issues or thoughts? I'm seeing my way to NOT running new 30A circuits, doing sanity check

Thanks!

[Peter Quinn]

I'm no electrician but I'd think running 19.5A on 12/2 20A circuit would be a poor long term strategy. I think the figure for motorized circuits is not to exceed 80% the circuits rating, so 20A gets you 3HP, not 5. Might it start and run the machines? Probably, but you'll be heating the wire beyond what is advisable over the long haul.

As far as receptacles , I like twist locks and strain reliefs on all my machines as my boxes are mostly ceiling hung, but in reality in a home shop it's of little importance as long as they match the current rating. I have some of both.

[Curt Harms]

I'd bet the saw wouldn't be an issue unless you're a commercial operation. How often do you use the full depth of the blade, and for how long at a time? If you were ripping 12/4 white oak nonstop you could have a problem. The cyclone could be more of an issue but if I had existing wiring I'd be tempted to try it and put a clamp-on type ammeter on it and see how many amps it actually pulls. It'd depend on ducting, filters if any, how many gates open etc. Of course if this is a permit situation, it's whatever the local authorities want. I'm not sure where and how the 80% rule comes into play. As long as the circuit breaker is working as advertised I don't think you'd be creating a danger, just causing nuisance trips.

[Jason White]

I use L6-20 plugs for 20 amp circuits and L6-30 plugs for my 30 amp circuits. Probably overkill to have the locking plugs in my home shop, but I figure overkill is usually better when it comes to all things electrical.

Hi all. I've recently purchased some 240V machines with 3-5HP motors. All came wired with locking plugs on them, 3 poles and ground (4 prongs), 20A plugs of type L1420P. Don't know why 3 poles, motors all require only 2 plus ground on these, I'd have expected L6-20P... My shop and machines are currently wired with non-locking 6-20P. Both are fine according to NEMA charts (here's a nice reference from previous thread at SMC asking about 240 v plugs: http://www.powercabling.com/nema.htm ) Question 1: Thoughts on using straight bladed plugs instead of locking ones currently on the machines, which would let me use my currently installed receptacles? Just personal preference it seems, but anyone have any supporting stories? Question 2: Can I replace these locking plugs on the 5HP machines and run them on 20A circuits, 12 gauge wiring with 20A CB to a subpanel I installed myself, without issues? Previously I just assumed that a 5HP motor would need a 30A circuit on 10AWG wiring, but now looking at the motor plates and seeing them all rated less than 20A, I'm thinking my 20A circuits are OK? Garage shop, hobby use. As I read the NEC, 12AWG can do 25A, over-current protection to be 20A. So I'm thinking if the machines don't trip the 20A, should be good? Here's the machines, motor ratings and motor faceplate or instruction manual amperage: SawStop ICS 5HP 19.7A from both motor plate and manual. Manual says saw should be wired with a 3 wire (hot/hot/ground) and NOT a 4 wire plug/cable, tells you to cap the neutral if you have 4 wires run. Oneida 5HP cyclone DC, 5HP Baldor, 19.5A, good at 20A if my CB can handle the start up (slow trip one). Also shows only 2 wires and ground on their motor wiring diagram. Anyone out there running these or other &quot;5HP&quot; motors rated just less than 20A on 20A circuits and have any issues or thoughts? I'm seeing my way to NOT running new 30A circuits, doing sanity check Thanks!

[Howard Acheson]

Straight or locking is your preference. I personally prefer straight so that the plug easily comes out of the receptacle if I trip over the wire. However, some seem to feel it's safer to not have the plug come out of the receptacle. Your choice.

Second, as to the amperage of the plugs, what does the equipment manufacturer recommend for plugs and wiring? All my 240 volt equipment is on 30 amp wiring and connectors and breakers.

[Steve Bracken]

Straight or locking is your preference. I personally prefer straight so that the plug easily comes out of the receptacle if I trip over the wire. However, some seem to feel it's safer to not have the plug come out of the receptacle. Your choice.

Second, as to the amperage of the plugs, what does the equipment manufacturer recommend for plugs and wiring? All my 240 volt equipment is on 30 amp wiring and connectors and breakers.

That set up allows you to draw 9.6 hp before you have to worry about a tripped breaker.

Most equipment for home and very light commercial runs less than 5 hp, so a 20 Amp circuit is more than enough unless more than one machine is run on the same wiring, at the same time, or someone has some very large machines

[Andrew Pitonyak]

If i were running wire, I would run 4 wire rather than 3 for the machines that support the 4 wire connection. May not really be needed, but, if I have a choice, I prefer the extra safety margin that it usually provides.

[Tom Godley]

If the manufacturer indicates that the tools will run on 20 amps then that is all you should need. People put all kinds of plugs on tools -- correct or not.

If this is new wiring -- you can always run 10g and still use 20amp breakers/ outlets.

The first time I wired a shop I used 10g for a select number of runs -- Just in case I needed to switch up to 30 amps. I have done that since -- and I have never needed more than 20 amp!. So its been a waste -- but I am a victim of habit

I never use 30amp feed for a 20amp tool. I like the spec grade twist lock plugs - only for the way they clamp down on the feed wire. I don't like using the screw.

[George Clark]

If i were running wire, I would run 4 wire rather than 3 for the machines that support the 4 wire connection. May not really be needed, but, if I have a choice, I prefer the extra safety margin that it usually provides. Today 12:34 PM

Andrew,

Could you explain the "extra safety margin." I was under the impression that the four wires are necessary if there are both 220v and 110v circuits being supplied. Supplying a 220v circuit alone requires only three wires.

George

[Steve Bracken]

Andrew,

Could you explain the "extra safety margin." I was under the impression that the four wires are necessary if there are both 220v and 110v circuits being supplied. Supplying a 220v circuit alone requires only three wires.

George

At a guess ..... Four wires does allow two discrete paths to earth in the event of a fault.

In a three wire system, the return and ground use the same wire.

[Andrew Pitonyak]

Disclaimer: I am not an electrician.... That said, I have expectations for a single phase system when running 220 to something:

Short answer, the fourth wire is ground (kind of like you rarely really need three wires for your 120V electrical outlet).

1. You have two 120V lines coming into your house.
2. You run the two 120V lines to the device. Lets arbitrarily say that one is red and one is black.
3. You run a Neutral (probably white). The neutral takes the electricity back to the box.
4. You run a ground (probably uncovered copper, but, ground is usually green on your equipment).
5. Ground is tied to neutral at the panel.

The ground is typically connected directly to the chassis and will only matter if there is a direct short. It is argued that you usually do not need the ground, but, it is safer to have it. Some equipment may have trouble if the ground is not present.

When I look at a big table saw and all of that nice metal, I really like to know that ground is connected to it in case there is a short.. You may usually need it rarely, but, when you do, your life may depend on it.

So, that is my rational. That said, I am generally risk adverse.

[Steve Bracken]

Disclaimer: I am not an electrician.... That said, I have expectations for a single phase system when running 220 to something:

Short answer, the fourth wire is ground (kind of like you rarely really need three wires for your 120V electrical outlet).

1. You have two 120V lines coming into your house.
2. You run the two 120V lines to the device. Lets arbitrarily say that one is red and one is black.
3. You run a Neutral (probably white). The neutral takes the electricity back to the box.
4. You run a ground (probably uncovered copper, but, ground is usually green on your equipment).
5. Ground is tied to neutral at the panel.

The ground is typically connected directly to the chassis and will only matter if there is a direct short. It is argued that you usually do not need the ground, but, it is safer to have it. Some equipment may have trouble if the ground is not present.

When I look at a big table saw and all of that nice metal, I really like to know that ground is connected to it in case there is a short.. You may usually need it rarely, but, when you do, your life may depend on it.

So, that is my rational. That said, I am generally risk adverse.

Risk averse, when dealing with 240V (often closer to 250 in practise), is a very good attitude to have.

120V rarely does more than offer a nasty experience. 240V can, and regularly does, kill people.

I have often felt that Americans are a bit too free and easy about electricity, probably because most grow up with relatively non-fatal power supplies.

Europeans do not make that mistake.

All equipment, unless full double-insulated requires a separate ground (three prong). Sure it will run if you ignore the ground, but it could kill you if it develops a fault.

Whole house GFCIs are a good idea too

[Peter Quinn]

I'd bet the saw wouldn't be an issue unless you're a commercial operation. How often do you use the full depth of the blade, and for how long at a time? If you were ripping 12/4 white oak nonstop you could have a problem. The cyclone could be more of an issue but if I had existing wiring I'd be tempted to try it and put a clamp-on type ammeter on it and see how many amps it actually pulls. It'd depend on ducting, filters if any, how many gates open etc. Of course if this is a permit situation, it's whatever the local authorities want. I'm not sure where and how the 80% rule comes into play. As long as the circuit breaker is working as advertised I don't think you'd be creating a danger, just causing nuisance trips.

That would be those pesky local authorities, I think they are called the NEC? I was speaking with the electrician we use at work during a RAS upgrade that I was responsible for installing. Motor name plate was 17.9A 220 and he wouldn't run it on 20A. He said there was a specific percent of available current that NEC allowed, after which the next size circuit had to be used. This is a commercial operation. I think he said 80% was allowed. You don't drive your car at red line all the time do you?

[Curt Harms]

That would be those pesky local authorities, I think they are called the NEC? I was speaking with the electrician we use at work during a RAS upgrade that I was responsible for installing. Motor name plate was 17.9A 220 and he wouldn't run it on 20A. He said there was a specific percent of available current that NEC allowed, after which the next size circuit had to be used. This is a commercial operation. I think he said 80% was allowed. You don't drive your car at red line all the time do you?

That would depend on how the red line was established. If the red line was established at 5000 R.P.M. and testing established that damage would occur at 6000 R.P.M. then no. If testing established that damage may occur above 10,000 R.P.M. but the manufacturer set 5000 R.P.M. as the redline to ensure longevity and reliability, then I would not regard operating near redline as all that risky.

More to the topic at hand, I don't know what the NEC would specify in this instance. Local jurisdictions can impose requirements more restrictive than the NEC. I'm pretty sure there'd be more risk to a 12 ga. wire carrying 30 amps for 8 hours than a 12 ga. wire carrying 30 amps for 8 minutes. The code likely accounts for continuous usage. Unless a circuit breaker fails, it's going to trip after several seconds of an over amperage condition.

[Mark Beall]

Disclaimer: I am not an electrician.... That said, I have expectations for a single phase system when running 220 to something:

Short answer, the fourth wire is ground (kind of like you rarely really need three wires for your 120V electrical outlet).

1. You have two 120V lines coming into your house.
2. You run the two 120V lines to the device. Lets arbitrarily say that one is red and one is black.
3. You run a Neutral (probably white). The neutral takes the electricity back to the box.
4. You run a ground (probably uncovered copper, but, ground is usually green on your equipment).
5. Ground is tied to neutral at the panel.

The ground is typically connected directly to the chassis and will only matter if there is a direct short. It is argued that you usually do not need the ground, but, it is safer to have it. Some equipment may have trouble if the ground is not present.

When I look at a big table saw and all of that nice metal, I really like to know that ground is connected to it in case there is a short.. You may usually need it rarely, but, when you do, your life may depend on it.

So, that is my rational. That said, I am generally risk adverse.

Umm, no. If you have 3 wires running to a 240V device, you have 2 hots and a ground. There is only a neutral if you also need 120V at that device, the neutral is the 4th wire in a 4 wire connection.

For those that don't understand how this works, look up "split phase electricity".

mark