Contractor Talk - Professional Construction and Remodeling Forum banner

1 - 18 of 18 Posts

·
Registered
Joined
·
1,260 Posts
Discussion Starter #1
I am trying to figure out what supply I need to tell my customer( who is an 800 mile plane ride away) they need to have ready for me to install their new machine. It is rated at 102full load amps 230v. Has a 15hp and a 20hp motor and some other small loads. The machine will not let both motors start at the same time.

My question is will a 100 amp supply breaker suffice? My electrical knowlage source will not be available till Monday. So I am asking here. My first two motor machine install.

I do have a 2014 NEC book if I knew were to look in it. Not that it applies in this case.
Thanks, Jim
 

·
Electrical Contractor
Joined
·
244 Posts
The NEC requires us to use Table 430.250. Generally for 2 motors you need to add them together and and take 25% of the largest. The table shows 42 amps and 54 amps which comes to 109.5 with the 125%

54*1.25= 67.5
67.5+42 = 109.5

You stated that the motors won't start at the same time but I assume they will be running at the same time. It looks like you may need to go with 125 amp. Not sure what the smaller loads add up to be.
 

·
Banned
Joined
·
2,622 Posts
will a 100 amp supply breaker suffice?

I do have a 2014 NEC book if I knew were to look in it.
The NEC deals with motors, cables, switches, etc.
It never hit me before, but it seems the makers of these products who want happy customers will interpret the NEC for you, for free, so in some cases at least you don't have to buy books or take courses.
 

·
Registered
Joined
·
7,076 Posts
If the manufacturer says that draw on full load is 102 amps, doesn't it make sense to have a circuit (and breaker) that will supply that, plus some headroom?
 

·
John the Builder
Joined
·
16,993 Posts
Wonder if these guys know where Guam is, that the major source of income is tourism.

The military installations aren't much help - ain't much military that meshes with civilian needs. Lots of contractors there - all they do is military and then go hit the local massage parlors.

Max start load times 125% and go from there.
 

·
Electrical Contractor
Joined
·
2,411 Posts
I am trying to figure out what supply I need to tell my customer( who is an 800 mile plane ride away) they need to have ready for me to install their new machine. It is rated at 102full load amps 230v. Has a 15hp and a 20hp motor and some other small loads. The machine will not let both motors start at the same time.

My question is will a 100 amp supply breaker suffice? My electrical knowlage source will not be available till Monday. So I am asking here. My first two motor machine install.

I do have a 2014 NEC book if I knew were to look in it. Not that it applies in this case.
Thanks, Jim
No, a 100A breaker is not good for a 102A load.

Wait until Monday to worry about this.

Please, leave the electrical work to those who know what they are doing.

And leave your code book in the office, or better yet give it to a sparky you know. You don't need it.
 

·
Registered
Joined
·
7,076 Posts
No, a 100A breaker is not good for a 102A load.

Wait until Monday to worry about this.

Please, leave the electrical work to those who know what they are doing.

And leave your code book in the office, or better yet give it to a sparky you know. You don't need it.
Seemed like a reasonable question to me. Maninthesea sells and installs certain equipment (big compressors?), and needs to inform the customer about the electrical requirements. His question is perfectly reasonable. Maybe it can't be answered on the information provided - that would be one answer.
 

·
Electrical Contractor
Joined
·
2,411 Posts
Seemed like a reasonable question to me. Maninthesea sells and installs certain equipment (big compressors?), and needs to inform the customer about the electrical requirements. His question is perfectly reasonable. Maybe it can't be answered on the information provided - that would be one answer.
If he's installing the equipment then he needs to be qualified to do the install. If he is also running the circuits to the equipment then he needs to be a qualified electrician as well. Based on the original questions the latter seems unlikely, so IMO he should NOT be doing the electrical branch circuit side of things. ESPECIALLY in a commercial/industrial setting.

The ONLY thing he needs to do is inform the client of the electrical specs, NOT how to wire it.
 

·
Capra Aegagrus
Remodeler
Joined
·
24,094 Posts
The OP doesn't indicate whether he's planning to run any circuits or not. On the contrary, it sounds like the client is to arrange that and have the circuit(s) in place and ready to be connected. I think Jim's probably well enough qualified for that step.
 

·
Administrator
Maker of Fine Sawdust
Joined
·
44,194 Posts
With a motor circuit usually the motor is protected by internal systems such as a motor starter.

Motor circuits are weird as the breaker can be setup for the wire current max or the inrush current. I've seen motors on 12 ga wire with 70amp breakers.
 

·
Contractor of the Month
Joined
·
26,075 Posts
If he's installing the equipment then he needs to be qualified to do the install. If he is also running the circuits to the equipment then he needs to be a qualified electrician as well. Based on the original questions the latter seems unlikely, so IMO he should NOT be doing the electrical branch circuit side of things. ESPECIALLY in a commercial/industrial setting.

The ONLY thing he needs to do is inform the client of the electrical specs, NOT how to wire it.
He needs to tell the electrician what to install for the machine...whats the problem?

I think in this case the only person who can answer the question is the manufacturer.
 

·
Electrical Contractor
Joined
·
244 Posts
He needs to tell the electrician what to install for the machine...whats the problem?

I think in this case the only person who can answer the question is the manufacturer.
Hopefully the electrician knows what to do.

Why is the mfg the only person that can answer the question. I believe I gave a code compliant answer and I must say that the mfg often give incorrect advise. I have run into that a few times.
 

·
Registered
Joined
·
1,260 Posts
Discussion Starter #17
Thanks guys. The MFR actuall answered my email on a Saturday which was great. His original email was a 100amp breaker might work but might trip every once in a while so recommended either going bigger or splitting he power supples. Then second email considered installation location and probability of voltage generally being low side recomended 125 or 150amps.

For the grumpy guys I have a better understanding than most on how electricity works, I was an electronic technician reactor operator in the navy. I forgot more than i remember. I use the NEC for wire size, & conduit size. I find no need to have an electrician run three wires & a ground from a power drop. Hate if you want. In the location this compressor is going I don't need any certifications nor NEC but I consider the NEC as a good guide. I do need to make sure I tell them what to have ready Becuase their "electrician" will generally be a guy from the PI that has a rudimentary knowlage.

Years ago I had the building owner fumeing mad at me Becuase I told them they needed 60 amp three phase and arrived to find single phase and refused to install. His reasoning was three wires = three phase deal with it.
 

·
Banned
Joined
·
2,622 Posts
His original email was a 100amp breaker might work but might trip every once in a while so recommended either going bigger or splitting he power supples.

Then second email. . .recomended 125 or 150amps.
He should have said somewhere between 50A and 300A may work. :laughing:
And he'd be right!

Sizing these things is supposed to be a matter of fact rather than a matter of opinion, the facts being dictated by physics and the constraints on what's allowed dictated by Codes.
WTF?

BTW, C'est Moi, I have to give you credit for showing how you got your answer.

12 ga wire with 70amp breakers.
Wiki gives #12 fusing at 5600A in 32 mS.
If a 70A breaker curve shows it tripping at less than this then it will protect the wire rather than the wire melting before the breaker trips.
 
1 - 18 of 18 Posts
Top