Conductor/Breaker sizing question

[rabler]

If it was me, assuming the main panel is a 200A service, I would use 2/0 SER wiring from there to the shop subpanel and a 100a breaker. The additional wire cost is going to be less than $100, and the convenience of having the additional capability down the road is significant if you get more or larger tools and/or the wife doesn’t give up the hot tub. There is no downside beyond the slight cost. If this is a DIY project just be sure to clean the aluminum wire ends and use anti-oxidant grease.

 

[Tomzo]

Thanks Bi11Hudson - just so I am correctly understanding your guidance here, you are saying to wire the conductors from the subpanel to the VFD at the input rating of the VFD (10A) plus 20% (so 12A). I am interpreting the second part of the guidance to mean the conductors from the VFD to the motor, which would be the rating of the machine load (motor) x 1.73 + wiggle room. I am not sure if I am interpreting this correctly or not.

Thanks

Tom

 

[Tomzo]

If it was me, assuming the main panel is a 200A service, I would use 2/0 SER wiring from there to the shop subpanel and a 100a breaker. The additional wire cost is going to be less than $100, and the convenience of having the additional capability down the road is significant if you get more or larger tools and/or the wife doesn’t give up the hot tub. There is no downside beyond the slight cost. If this is a DIY project just be sure to clean the aluminum wire ends and use anti-oxidant grease.

I do have a 200A panel but it is so packed with wires I am not sure I could squeeze in 2/0 conductors, but you have a good point there. We had solar put in about 5 years ago and boy did they mangle the panel wiring. They needed more space so they put in some double breakers for the smaller circuits and rather than clean up the wiring to appropriate sizes they just looped it around in there. I squeezed in a 30A plug for my RV last year and it was a bear to get in there. The cover barely fits on at this point. I have #6 wires coming out now for the hot tub and for simplicity's sake, and to avoid having to pay an electrician to come out and properly clean up the panel, I had planned to use the same conductors that come from the panel and through the rafters in my garage to a j box that is located in the garage rafters. I would re-route those wires to the panel and then bring new #6 wires back to the j box from the relocated GFCI breaker in the subpanel.

I was a building inspector in the 90's and have done a good deal of electrical work, so I am pretty familiar with household wiring principles and basic code requirements. I have installed subpanels before including another 50A subpanel for my pool and pool control system that was permitted and inspected. Getting nice clean wiring in a crowded main panel is not a skill I possess though, so that part I would leave to an electrician who does this all the time. Perhaps a steak dinner for my electrician friend is in my future.

This sort of dialog is why I appreciate the communities that surround my various hobbies. I appreciate the loads of good advice in this thread. The trick here is getting this done without breaking the bank - my wife's tolerance of my pursuits does have its limits both in terms of time and money!

 

[Bi11Hudson]

Thanks Bi11Hudson - just so I am correctly understanding your guidance here, you are saying to wire the conductors from the subpanel to the VFD at the input rating of the VFD (10A) plus 20% (so 12A). I am interpreting the second part of the guidance to mean the conductors from the VFD to the motor, which would be the rating of the machine load (motor) x 1.73 + wiggle room. I am not sure if I am interpreting this correctly or not.

Thanks

Tom

What I was trying to convey is that the 3 phase load (VFD to motor) will be as the load (motor) is rated. From the source to the VFD (single phase) will be 1.73 times the name plate rating of the motor. On top of that, add a little wiggle room, both from the source to VFD and from the VFD to the motor.

In both cases, the NEC requires circuits to be loaded with a normal maximum of 80% of the breaker rating. That's where the 20% wiggle room came from. You already have that where your VFD is rated larger than your motor. I'm more concerned about from the source to the VFD. When you convert the single phase to 3 phase, the power has to come from somewhere. The 1.73, square root of 3, is the accepted factor for calculating single phase to three phase conversion.

It is just my opinion, but from the sounds of it your solar conversion was done by a wireman, not an electrician. The state doesn't draw a distinction between the two. Both can get a license. I have never had a license as such, but in industrial work as an inhouse electrician, a wireman doesn't last very long. And sometimes gets somebody killed. . .

You can clean up your panel yourself, if you're not nervous about it. Once you turn off the breakers, it's just a piece of wire. But if it's fed from the solar as well, it's still hot with one breaker off. Other than that, you kill the breakers, cut the wire shorter, and put it back where it came from, dressing the wire as you go. Electricity isn't dangerous as long as you know what not to do. If you don't know that, your electrician will. And can do the job for you.

Putting larger wires into your panel is something that any residential wireman can handle. And likely does on a regular basis. You might want to 'up the ante' a bit though, as it is more work. But if you expand, be sure to do it right so it can be expanded again later. The individual details would mean very little to you, but your electrician already knows them. Or should. . .

When I bought my house, it needed to be rewired. Built in 1887 or so, it had 120 volts 30 amps service from around 1920. I put in a 250 amp 240 volt panel, a Sq. D type QO 42 slot panel. And filled it. . . After 45 plus years, I have 3 outbuildings and 2 panels of 100 amps each. Fed off of one 75 amp submain. Only one because I can only be at one or the other at any given time. And never run a machine unattended. My generator is only good for 30 amps at 240 volts. And my solar is completely independant of the incoming line.

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[sdelivery]

With everything I have read hear I would suggest you get a local electrician that is experienced in what you require.
I am not trying to frighten you or discredit the well meaning help you are receiving here.
Electrical fires are common when things are not done correctly.
Codes change frequently and they may not be the same in my area as in yours.
Some things are best left to experienced professionals....you are gambling with your house and your families lives.

 

[Tomzo]

With everything I have read hear I would suggest you get a local electrician that is experienced in what you require.
I am not trying to frighten you or discredit the well meaning help you are receiving here.
Electrical fires are common when things are not done correctly.
Codes change frequently and they may not be the same in my area as in yours.
Some things are best left to experienced professionals....you are gambling with your house and your families lives.

I am fully aware of the risks - hence my posts here. I am always very careful when I do electrical, not just about the hazards of working in panels, but also to get the circuits designed properly and installed with all appropriate safeguards. I have about a dozen circuits in my home that I have installed from the panel or modified over the years to move outlets, switches, etc, so my confidence is pretty high that I can do it safely. But, as this project has been expanding in scope I will bring in someone who does this for a living to at least guide me if not do the work.

 

[Tomzo]

FYI - I have an electrician scheduled to come by this week to give me a price to clean up the panel and get the new subpanel fired up. My buddy was unavailable unfortunately.

 

[Bi11Hudson]

Electrical fires are common when things are not done correctly.
Codes change frequently and they may not be the same in my area as in yours.
Some things are best left to experienced professionals....you are gambling with your house and your families lives.

Electrical wiring is not something to be taken lightly. I have seen "code" work by a "licensed" journeyman that failed within a couple of days. Remember that the code is not a standard to work to, it is the minimum acceptable to the local authority. Workmanship "to the code" is done because time is money. Paying someone to come in to do the work, the work meets these minimum standards. Sometimes doing it right, as opposed to code, takes longer, hence more money. Since you are paying for "cleaning up the panel", you will likely get a better job.

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[sdelivery]

If you have read and tried to work to the ever changing NEC and state and local codes you will not do shoddy work.
There is a whole section on workmanship that includes items like to much wire, looping and other rats nest makers.
But, you have to read and apply what's there.
I doubt your job that failed was done to code.
More than likely an abbreviated portion of some of the code.