UL, Insurance, fire and VFD/Spindle

[ed_lang]

I was told last week that using a spindle on single phase power, will only net you 3.25HP no matter what size spindle you have. I was also told that using an oversized VFD to generate the 3 phase power for a 4hp HSD (or larger) spindle will only net you 3.25hp and it is not an approved combination for UL or the insurance. Well, I just don't know about any of this. Do you?

I see several manufactures that will sell a 4hp HSD (or other spindle) with a larger VFD, to be connected to single phase power.

I also have talked to some that will not sell over a 3hp spindle and VFD due to the above question I have asked.

If a rotary phase converter is installed and 3 phase power is run to the VFD, then it seems that everyone I talked to was happy and said it is an approved installation.

I would like to hear from folks who know the answer. Please no "in my opinion".

This may well affect many of CNC owners so it is important to get this correct.

I will be watching and researching.

[cabnet636]

ed i have it both ways the electrician is coming monday for more work so thanks i will ask!!

jim

[dana_swift]

Ed.. there is no fundamental reason for any limit to horsepower due to the power being single phase.

Individual VFD's have limits as to how much power they can deliver. The VFD/Spindle is the limit, not the single phase power. You could build/buy a VFD/Spindle to develop any horsepower you wish with single phase as long as the electric company can run big enough wire to your shop.

If that is a good enough answer, stop reading! What follows is my electrical engineering background talking.

One horsepower is 746 watts.

With perfect efficiency, At 220 volts single phase each horsepower draws 3.4 amps. (3.4 = 746/220)

Anything developing 3.25 hp will draw 11.4 amps (11.4 = 3.4*3.25) at 220 volts + some extra current for friction and other losses.

With a 15 amp breaker the physical (non/reactive) limit is 3.25Hp. The limit is the breaker in this case, not single phase. Have an electrician wire in a 40A circuit then the horsepower limit becomes something around 11hp (non-reactive load) and around 5Hp (reactive load).

Real spindles are motors, so they are reactive- so there are other factors to consider which does reduce the real horsepower available.

The only electrical difference between 3 phase and 1 phase as far as Hp is concerned is the efficiency of the power supply system.

The physical limits are determined by:

1) Your circuit breaker size
2) The length and gage of wire in the circuit
3) The power factor of the VFD
4) The power limit of the VFD

The limit will be due to the VFD's ability to deliver current to the spindle, not the single phase input of the power.

UL and insurance is another matter, they may not trust us with large amounts of power. That can be settled with another policy.

Hope that makes sense-

D

[ed_lang]

Dana, thank you for your answer, but my question is not can it be done as I know it can, but rather is the legal and with blessings from the insurance stand point.

I can remember my grandfathers house had wires run through joist with ceramic tubes for insulators... It worked, but would not pass "code" now, but did then. It was called knob and tube.

I do appreciate your efforts!

I am still waiting for an answer from someone.

[myxpykalix]

"is the legal and with blessings from the insurance stand point"

Seems like that is a question for the insurance underwriter however i doubt that they have the technical knowledge to answer that question. Maybe they have someone in a industrial underwriting division that might have the expertise.

I had a tennant who worked on industrial applications at Uva and other places and he worked single phase, 3 phase, 770, ect. You might call one of the local bigger electrical contractors and see if they would answer some of your questions.
Don't you have any contacts still at Uva that might be of help?
Here is a link for a industrial electrician from local craigslist
http://charlottesville.craigslist.org/sks/1349932663.html
He has 35 yrs experience i would bet he has dealt with inspectors and underwriters ect.
hope that helps....

[jerry_stanek]

I would think that they would not be allowed to sell a unit that is not UL approved.

[dana_swift]

My experience with insurance companies is they will insure anything if you are willing to pay a high enough premium, and they are reasonably assured to not have to pay any money out.

Meeting NEC requirements should be adequate for the insurance requirements. NEC codes exists because of the real needs for safety, which is the concern of the insurance companies also. If you can get an electrician to install it, the local inspector to approve it, then the insurance company should have no reasonable reservations.

That is just my opinion however.. I'm not an underwriter!

D