Wire size for 200A Subpanel

[sansbury]

Discussing this with my electrician and I’d like to have some additional opinions:

We are pulling service from a second meter on my house (weird but how National Grid wanted it done) through my basement and out via 2” conduit to the new building. Probably about 150’, round up to 200 to be generous.

The subpanel is rated for a full 200A to feed a 20HP Phase Perfect for a CNC mill.

My electrician said he was planning to pull 4/0 aluminum and that it was sufficient for purpose. I asked what copper would cost and he said “a LOT more,” implying he’d also have to run additional conduit through my basement so more than just additional material cost.

Running through online calculators it seems like I’m looking at 4% vs 2% drop for each conductor.

I’ve heard voltage drop can be an issue with these machines. Mine will alarm out below 190V. It seems like I’d have plenty of headroom above that, but I’m not a professional so don’t want to assume.

For a couple thousand I’d upgrade for sure but not sure if it’s going to be a lot more, and don’t want to spend money if it’s not truly needed.

 

[BrandonV]

250ft of 3/0 Cu SER is going to be over $5k.
250ft of 4/0 Al SER is probably close to $1k.

Just a rough estimate of how much more copper costs these days.

There is always the option of asking him to use 250 Al. From the source to the furthest location you shouldn't really exceed 5% voltage drop in total.

 

[Bert_]

Last fall I wired a second 15hp fan to a 450' run 4/0 alum. 240v 1ph.

Total of 30hp. Voltage dips to around 190 when starting the second fan. Stays about 220v when both are running.

 

[mm08822]

The online specs for a 20hp pte version indicate 111 amps max. 4/0 AL will carry that at 200' under 3% vd.
What are the other loads served by this new 200amp panel?

But, w/o looking up the requirements in NEC for a service running thru another building to feed an adjacent building, I expect you will need at a minimum:
Disconnect with ocp at the meter,
The reduction of service conductor size does not apply....so 4/0 AL for 200a is not permitted,
Will require a 4-wire feed to 2nd building.

Is your POCO aware of this load?

So 4/0 AL is way undersized to support a 200a service with other expected loads and at 200ft.

You need a load calc for the entire new building as a starting point , then contact your POCO.

 

[sansbury]

Is your POCO aware of this load?

What do you mean by this?

 

[sansbury]

What are the other loads served by this new 200amp panel?

There will be a mini split and a 20A/220 compressor. The rest will be intermittent loads as typical of a one man shop, so I might run a welder on a 50A circuit but not at the same time the CNC is running.

The machine is a Haas, and everyone I’ve talked to says they rate their machines very generously. Basically 200% peak capacity vs 100% duty. A lot of people run them on 60-100A breakers without problems and for how I work I will not be running it hard. But they will fault at 190V so I don’t want to cut that too close.

 

[mm08822]

Generally, unplanned loads of 7.5 hp and greater are not welcomed on 120/240v delivery systems by POCOs.

They may have to perform infrastructure upgrades to support the 20hp load.

You need a design review with the POCO first. Get your load calc done first.

 

[wyliesdiesels]

What do you mean by this?

Most PoCos have HP limits on single phase services. you should check with them first to see if theyre ok with a 20hp load on the service.

 

[wyliesdiesels]

4/0 AL definitely not rated for 200a. you need to go 1 size up.

 

[sansbury]

Ok, well, it sounds like I have a real mess to hack my way out of.

Thanks, I guess.

 

[mike93lx]

I'll be surprised if they let you run a 20hp motor. It's not an issue of running amps, it's all about startup

 

[Bert_]

I'm surprised you guys have so much trouble with small motors.

Here they don't blink an eye at a 15hp 1ph motor. I think the last time the one utility wanted to do a line study, we were planning to run 150hp total on 240v 1ph.

 

[Bert_]

If your load is 180a or less you can use 4/0. There is no 180A breaker so you can put it on a 200A. I can pretty much guarantee you will never pull that much.

20hp is only 80-90 amps

 

[mike93lx]

I'm surprised you guys have so much trouble with small motors.

Here they don't blink an eye at a 15hp 1ph motor. I think the last time the one utility wanted to do a line study, we were planning to run 150hp total on 240v 1ph.

In residential? Feels like you are talking about a farm?

 

[Norcal]

If the load is 180A or less 4/0 AL alloy can have a 200A breaker, if copper it will need to be 3/0 CU, because 2/0 CU is 175A & is a standard breaker size, 180A is not so the next size up applies.

 

[Bert_]

In residential? Feels like you are talking about a farm?

The only difference is you probably won't share a transformer on a farm.

 

[mike93lx]

The only difference is you probably won't share a transformer on a farm.

Pretty big difference, no?

 

[Bert_]

Pretty big difference

If you're spending money to set up a machine shop, a few thousand for them to hang a transformer shouldn't be a big deal.

 

[mike93lx]

If you're spending money to set up a machine shop, a few thousand for them to hang a transformer shouldn't be a big deal.

No argument.

My poco requires consult when a total of 15hp is hit, not just a single motor. These requirements tend to be a surprise to most people here, so I bet the vast majority of the public have absolutely no clue that there is a requirement or process for it

 

[PCustoms]

No argument.

My poco requires consult when a total of 15hp is hit, not just a single motor. These requirements tend to be a surprise to most people here, so I bet the vast majority of the public have absolutely no clue that there is a requirement or process for it

7.5hp here, and based on the age of the line/transformer snaking through the woods I bet that would dim the neighborhood at startup

 

[mike93lx]

7.5hp here, and based on the age of the line/transformer snaking through the woods I bet that would dim the neighborhood at startup

Mine also has a restriction on voltage drop, specifically noting lights flickering/dimming, so the 15hp isn't a hard and fast rule.

 

[mm08822]

If your load is 180a or less you can use 4/0. There is no 180A breaker so you can put it on a 200A. I can pretty much guarantee you will never pull that much.

20hp is only 80-90 amps

The spec for that converter says 111 amp max. It is a digital device, not electro-mechanical.

 

[mm08822]

>7.5hp isn't prohibited necessarily, you just need to get alignment with the POCO. Maybe they have an issue, maybe not. It really depends where you are connected onto the grid and if anyone else gets impacted.

Not every POCO uses 7.5 hp as the limit. You have to read their posted service requirements.

 

[mm08822]

Another thing to minimize spikes/sags from the converter is to change ramp rates used in the CNC mill. I doubt it will ever ramp up like a motor on an across the line starter.

 

[mm08822]

OP, here's the playbook (assuming I found the correct POCO):

https://www.nationalgridus.com/media/pronet/constr_esb750.pdf Section 8 has specifics.

 

[wyliesdiesels]

I'm surprised you guys have so much trouble with small motors.

Here they don't blink an eye at a 15hp 1ph motor. I think the last time the one utility wanted to do a line study, we were planning to run 150hp total on 240v 1ph.

its a common issue in cities. not every PoCo is the same so you really shouldnt be surprised. my PoCo definitely has a limit. you go over that and they make you get 3Ø

also it sounds like youre talking about rural farm areas. we are not in the same setting as you. apples to oranges

 

[wyliesdiesels]

If your load is 180a or less you can use 4/0. There is no 180A breaker so you can put it on a 200A. I can pretty much guarantee you will never pull that much.

20hp is only 80-90 amps

he is running more than just a 20hp motor.

 

[wyliesdiesels]

OP, here's the playbook (assuming I found the correct POCO):

https://www.nationalgridus.com/media/pronet/constr_esb750.pdf Section 8 has specifics.

looks like 6.5HP might be the limit

 

[sansbury]

My utilities here are underground and served by a pad transformer. It’s right across the street from me. No, I’m not in the city, edge of small town.

Not sure of the KVa rating off the top of my head but there are maybe 3-4 houses in it.

The machine builder I’m buying from has a smaller machine that specs a nominal 7.5HP motor but it calls for a 40A supply so I think that 7.5 is maybe a bit generous on their part.

 

[wyliesdiesels]

The FLC for a 7.5HP motor is 40a and of course the nameplate FLA is lower so that is about right.

 

[sansbury]

I was looking at the chart in that doc which seemed to suggest that the upper “free” limit was 240/60A. If a 40A rated motor is definitely kosher then my worst case scenario is mild.

 

[mm08822]

From my observations, the ubiquitous green pad mount xformers are 25Kva. Maybe 30.

You will piss off your neighbors running that converter unless it's at 3am.

 

[mm08822]

So what are the specs on the cnc machine and the biggest motor it has on it?

Next, how was the 20hp phase converters size determined?

 

[BrandonV]

What do you mean by this?

Depends. For example the utility I've done consulting for doesn't have a hard limit (for residential that is) but if we notice that when you start your motor up it causes the voltage to deviate from the guidelines set by ANSI C84.1 you'll get a polite knock.

Other utilities have a hard limit.

 

[sansbury]

This is the machine:

https://www.haascnc.com/machines/vertical-mills/vf-series/models/small/vf-2ss.html

It’s nominally a 30HP spindle but it’s widely understood that Haas rates their spindles at a 200% intermittent capacity level, so the rating is extremely generous. Many people run off single phase in home shops and the 20HP Phase Perfect seems to be the most popular option.

I have a number of people on Practical Machinist saying they run these on as little as a 50A single phase breaker feeding a converter. I don’t doubt them. I just don’t know how much of a dice roll it is. For the money entailed I would want a pretty decent assurance.

 

[ericm]

Just for comparison purposes the utility at my Oregon place wants to know if your motor's over 3hp. I think at the California place it's 5hp.

 

[Bert_]

From my observations, the ubiquitous green pad mount xformers are 25Kva. Maybe 30.

You will piss off your neighbors running that converter unless it's at 3am.

Way to generic. 25, 37.5 and 50kva are all really common sizes for 1ph pad mount transformers. They all look the same

 

[Snapped-off]

This is the machine:

https://www.haascnc.com/machines/vertical-mills/vf-series/models/small/vf-2ss.html

It’s nominally a 30HP spindle but it’s widely understood that Haas rates their spindles at a 200% intermittent capacity level, so the rating is extremely generous. Many people run off single phase in home shops and the 20HP Phase Perfect seems to be the most popular option.

I have a number of people on Practical Machinist saying they run these on as little as a 50A single phase breaker feeding a converter. I don’t doubt them. I just don’t know how much of a dice roll it is. For the money entailed I would want a pretty decent assurance.

I know we got a lot of guys with some real cool gear here. But... "home shop" and a $72k bare bones CNC is hilarious.

 

[mm08822]

Way to generic. 25, 37.5 and 50kva are all really common sizes for 1ph pad mount transformers. They all look the same

Agreed, they can vary within the same enclosure size.

But the 25kva is pretty standard by me and typically feeds 4 homes in developments.

Also this area has ng for heat and appliances. All electric neighborhoods could easily be 30 or 50.

 

[Dagny]

Running 250s wont break the bank but I think the neighbors wont be happy no matter what you do.