Electrical question

[chvet73]

The other day at work an inexperienced electrician (he has only been doing electrical work for about a year) arrived to wire a new machine for our Woodshop. The shop has a 220v single phase outlet, 50 amp circuit, which is setup to plug a door machine into when needed. That's basically a shaper with 2 heads, which can cut raised panels and stile or rails. Big 5hp motor which draws about 40 amps. The new machine is a muti spindle drilling machine which does hole for european hinges or shelves. That machine draws only about 10 amps.
Now here's the question, the electrician said you could not run the drill on the same circuit as was used to run the door machine. Am I nuts but I don't see an issue running the drill on a higher amp circuit. Just because it can provide more amps it's only going to provide what it draws. Or am I wrong? Just thought it was an interesting question. The electrician wanted to add a lower amp circuit just for the drill.
Sorry for the long post but I wanted to try and explain what I was asking.

 

[buickanddeere]

Depends.
As long as the wire size on the drill is large enough up to the drill's switch from the plug. And the drill is equiped with overload/thermal protection. All is fine.

 

[Martinfan]

Your inexperienced electrician is right. You should run a seperate circuit for the lower amperage drill, otherwise the drill will not be fully protected, at the stall amperage, which could drastically damage drill. If the shaper is no longer in use, then just changing the circuit breaker to a lower amp breaker will be sufficient, as the wiring will be of ample size for the amp load.

 

[buickanddeere]

The 50 amp breaker is short circuit protection.
Motor loads with thermal protection will not burnout. That 50 amp panel breaker is to trip short circuits. It's not for thermal protection of motors.

 

[Ken-Pa]

Machinery manuafacturers post all electrical info on a tag for their protection & yours .I was a residential & light commercial certified electrician for 25+ yrs & I"ve been in similar situations where a customer wanted things done his way & didn"t care what codes were violated in the process . Now if the electrician hooked it up as you wanted him too , who would you hold responsible if the machine malfunctioned but didn"t trip the breaker before further damages occured ,or possible injuries occured to an operator ? Why sure, the electrician since he got paid & should know the correct wiring procedure . I learned that its better to walk away from a job if the owner refused to accept my knowledge of correct wiring . You need to show the guy appreciation for not wanting his carreer & reputation ruined by this one job .There"s always someone out there with no insurance & aims to get a quick buck . HTH! God bless

 

[Anonymous-0]

5 hp motor draws 26 amps.I run one on 30 amp td fuses with no problem.

 

[Dusty MI]

I had a customer want me to wire an exhaust fan in a window with an open frame motor in a class 1- division 1, paint mixing room. I refused and my boss agreed with me. Told me to finish what was needed and get out. While I was finishing the contract work the inspector came in. The customer was showing him around saying nothing was going to be flammable. They were going to be making latex paint. The inspector came up to me and asked what was going on? Why was everything Class I Division I. I told him I was doing as I was told by my boss.

Then they were mad at me because I had ratted on them.

We never got another job in there again.

I found out latter that the Fire Marshall had deemed it needed to be Class I Division I.

A few months latter they were making very flammable epoxy paint.

Dusty

 

[87nassaublue]

It sounds like what he was trying to say is you can't run both machines off that circuit safely at the same time. If the drill is 3 phase at 10 amps, the 50 amp circuit will barely see it there. There will be no risk of circuit overload unless you have a complete short in the drill which will most likely just burn out the armature of the machine that is bad anyway.

You have to remember, times are tough and he was probably trying to sell you another job that you can probably live without. I'd imagine he was short of cash and wanted more work.

 

[MarkB_MI]

If it was my shop, I would want them on separate circuits. With the 50 amp circuit you have a nice 20 percent margin for the 40 amp machine that goes away when you start the smaller one. If the the two machines need a total of 50 amps when running, the current draw will exceed 50 amps when starting the larger machine while the smaller is running.

How often would you expect to run the machines at the same time? If the answer is "almost never", then I'd say go ahead and tap into the 40 amp circuit. Otherwise run another line. Of course, the electrician wanted to sell you some more work, but his advice was sound.

 

[Anonymous-0]

The flex cord to the smaller tool won't be protected on the 50 amp circuit. Yes it will supply the tool, but may not protect the tool either. If something damages that cord it will ignite its surrounds on the 50 amp circuit. It may trip a lower current breaker before it ignites. The NEC presumes the flexible cord is protected by the branch circuit breaker, that's partly why you don't see 18 gauge extension cords anymore.

Gerald J.

 

[Ken-Pa]

Yep, that's how some of those people work . Its best to walk away than get into a lawsuit because he lied to the fire marshall or Ins co that you did inferior wiring which caused a fire or death . My motto is : do it rite or not at all . God bless

 

[87nassaublue]

If this were a hard wired piece of equipment, I'd agree but he did mention that this was a piece of equipment that is intermittently "plugged in" so I'd have to disagree. The circuit breaker in the breaker panel is not intended to protect the wiring of any external appliance, unless it is hardwired in and becomes part of the facility. It is designed and specified by building code to protect the wiring in the wall, (fire prevention) not the wiring of the appliance "plugged into" and external to the wall outlet. External appliances such as motors, etc., are required to have built in circuit breakers or thermal overloads interrupts to protect them. No one can anticipate what device someone might decide they want to plug into a wall outlet once the building has been constructed and the wiring installed. That being said, if someone chooses to downgrade a circuit breaker, to protect a "plugged in applicance" that would be by choice and not a requirement.

 

[Anonymous-0]

No, protection of the plug in cord is part of the NEC. In England all plugs have fuses to protect the cord but we don't do that in the US, so depend on the breakers to protect the plugged in cord.

Gerald J.

 

[buickanddeere]

If the cable and plug over to the shaper is heavy enough.And the shaper has it's own short circuit AND thermal/overload protection. Then yes.
A lot of people assume a panel breakers is thermal protection for motors. It's not that's what the thermal trip in the motor or motor starter is for.
The panel breaker is there for short circuit protection from line to line or line to chassis shorts.
A motor with a FLA rating of 10amp can legally use a breaker up to 20amp, time delay fuse of 20amp and a non time delay fuse of 30amp.Thermal/overload protection are to be set at 12.50amp.

 

[John T]

Sure, theres a time and place for over design or overkill to reduce voltage drop (like bigger then required wiring) BUTTTTTTTTTTTTTT a branch circuit protective device (in general while subject to motor exception noted below) MUST PROTECT THE CIRCUITS FEED WIRES FROM OVERHEATING/OVERCURRENT. If theres a branch circuit with 50 amp rated wire then a 50 amp circuit breaker in the panel will NOT allow more current then the feeder wires can safely handle without overheating (alls well) HOWEVER if somewhere in that circuit such as say a drop cord of only smaller No 10 wire is used from a safety switch to the appliance THAT WIRE IS NOTTTTTTTTTTT PROPERLY PROTECTED (by a 30 amp protective device) i.e. the 50 amp breaker in the panel will allow 50 amps to pass through wire thats only designed for 30 amps AND IT CAN OVERHEAT AND DEGRADE THE PROTECTIVE INSULATION....

If you want to run 50 amp wire from a 50 amp circuit breaker thats okay and then a wall mounted fused safety switch can be fused at 30 amps if its to supply smaller 30 amp wire to a load..........THATS HOW I RECOMMEND YOU DO IT so BOTH the 30 amp and 50 amp feed wires are properly protected. Also in some motor circuits dual element time delay fuses can be used to allow the motor to start (higher then running current when starting remember)

A typical motor feeder branch circuit will have feed wires protected by a breaker to match the wiring used and the load (short circuit protection) and then the motor will have a starter and/or thermal overload device to protect the MOTOR from overheating and damaging the expensive windings. i.e. theres "short circuit" protection (breaker in panel) plus "thermal overload protection" (often in a stand alone motor starter or an internal thermal overload) to protect the motor...

NOTE the code (motor exceptions) does allow a bigger circuit breaker IF NECESSARY TO ALLOW THE MOTOR TO START even where its not the normal sized breaker such as a 30 amp one and 10 gauge wire because they figure if theres a dead short the breaker will trip while the motor is protected by another thermal overload device.....

Its been yearsssssssss since I designed and specified branch circuits so no warranty, but I believe this to be correct....

John T
Untitled URL Link

 

[Denny 5]

There is some information that needs to be know to give an accurate answer. We would have to get this off the nameplate on the new machine. Does the new machine need a starter/controller, it will need a disconnect of the right size. You will need appropriate sized protection for the feeders for the new machine. From the limited information given you could even assume it is wired with # 14 wire as it only draws 10 amps. Without more information I would say your electrician is right in his answer.

 

[chvet73]

Thanks for all the replies. The issue just got me to be curious.
This was not a sell the job issue as he is an in house electrician, we all get paid by the source.
As to the question would both machines run at the same time, the answer is no. Only one would be plugged in at a time.

 

[David G]

It is nice to hear the people on this post talking code, instead of what will probably work.

I did notice one person below stated the 5HP motor FLA is 26-28 Amps, that is probably what the 50 Amp breaker is for. A 10 HP motor is 50 Amp FLA.

 

[Errin OH]

The issue you may want to look at is two fold,

1) If it pulls 40 amps and melts down is it really protected?

2) If it was you that was going to be sued for burning down the shop, what would you do?

 

[David G]

Breakers should protect only the wiring and interconnection devices. Overload protection still needs to be on the motor, or inline in addtion to the breaker.

All wiring and components need to be sized for the breaker.

 

[barn E]

1968 NEC addressed this under "tap rule" Less than 20 amp wiring shall not be allowed as a tap on 50 amp circuit. So 10 amp tap is not permitted. Reason probably is that the wiring tapped on is too small to be allowed the possibility of handling 50 amps. I am certain if you consult a new code book you can find the same restriction under "tap rule". I remember rewiring this type of violation in machine shops.