Why was this VFD wired this way?

[ching0n]

I'm looking to replicate this wiring scheme for a VFD (off a Grizzly lathe) and can't quite figure out why they used a step down transformer 110VAC-> 24VAC. As far as I can tell, it's just going to the control switches and can only surmise it's for shock prevention and/or lengthening longevity of the switches (though wouldn't that be an amperage not voltage thing?). At first, I thought maybe they needed 24V for a fan or the contactor or the relay but it doesn't look that way on closer inspection.

Basically, I figured I could simplify this some by using 110VAC but if there's some NEC regulation requiring 24V at panels, maybe I'll stick with that. As far as I could tell, the switches they used are 120v+ rated so I'm a bit stumped.

 

[Steve from Socal]

The controls are 10 volt from the VFD, the speed sensor and display need 24V?

 

[ching0n]

The controls are 10 volt from the VFD, the speed sensor and display need 24V?

The 10V AC output/input is for the remote potentiometer being fed by/to the VFD. By controls I meant the on/off/e-stop/fwd/rev switches, sorry I didn't clarify. I think you may be correct about the spindle speed control board/display though....I'm not using those so might be able to ditch that side.

 

[Bert_]

Seems like a lot of wiring for only a few functions. Start/Stop, fwd/rev, and speed control. All that can be done directly with the inputs of the vfd.

 

[Firebrick43]

They did it for the contactor, which is connected to the Estop switch and kills all the motors, not just the spindle that the VFD is hooked up to. And they have the switches hooked up correctly.

Not really sure why the fan couldn't stay on but the way they did wire it is probably about as safe as it can be, if we ignore the lack of craftsmanship in wiring it.

This is how most industrial equipment would be wired, at least schematically. Most of the time they don't kill power(just send the drive into e stop mode) to the VFD itself as heavy loads can be braked faster thru the VFD and braking resistors attached to the VFD but this is a little lathe?

I am not sure that 110v control voltage is forbidden but I have not seen a new machine with it in 20 years. All the stuff I worked on that was 110v control voltage was 1980 and prior build. And when we recontrolled them it was changed to 24v dc. That is the standard. You don't need to worry about shock below 50v DC

 

[larry_g]

Basically, I figured I could simplify this some by using 110VAC but if there's some NEC regulation requiring 24V at panels, maybe I'll stick with that. As far as I could tell, the switches they used are 120v+ rated so I'm a bit stumped.

There many not be a NEC rule on this but remember that these machines end up in other parts of the world where the requirements may be different.

lg
no neat sig line

 

[ching0n]

Seems like a lot of wiring for only a few functions. Start/Stop, fwd/rev, and speed control. All that can be done directly with the inputs of the vfd.

That's all most of this wiring is really doing, feeding the inputs to the VFD remotely w/the added provision of a fuse, contactor & cooling fan for the motor & enclosure, which I want. Currently I'm running the VFD off the panel but want to enclose it to prevent chips getting into it. The manual also calls for some of these things that are the bare minimum (contactor, relay, fuse, etc...) I think the fuse here isn't feeding the VFD but rather the spindle control board.

 

[micromind]

One possibility is that the amount of current on the VFD 24DC controls is small enough that, odd as it may sound, it won't work with pushbutton contacts the have been used with higher currents.

There's not enough energy to blow the contacts clean and even the slightest amount of contamination will cause a failure.

24AC controlling a relay that has bifurcated gold contacts will solve the problem. The gold contacts can handle very low current.

 

[ching0n]

They did it for the contactor, which is connected to the Estop switch and kills all the motors, not just the spindle that the VFD is hooked up to. And they have the switches hooked up correctly.

Not really sure why the fan couldn't stay on but the way they did wire it is probably about as safe as it can be, if we ignore the lack of craftsmanship in wiring it.

This is how most industrial equipment would be wired, at least schematically. Although many times they don't kill power(just send the drive into e stop mode) to the VFD itself as heavy loads can be braked faster thru the VFD and braking resistors attached to the VFD but this is a little lathe?

I am not sure that 110v control voltage is forbidden but I have not seen a new machine with it in 20 years. All the stuff I worked on that was 110v control voltage was 1980 and prior build. And when we recontrolled them it was changed to 24v dc. That is the standard. You don't need to worry about shock below 50v DC

ah, you're right....I'm new at wiring contactors and just realized A1 & A2 is the control....they're available in 120v AC though no?. I figured this schematic was the 'simplest' I could get away with and do it correctly. If I'm ditching the spindle control board feed do I need an 8 pole contactor?

I think w/flood coolant being a possibility, 24 seemed sensible too.

the one in question:

 

[Firebrick43]

Looks like the Industrial machinery standard, NFPA 79 still allows 120v ac max at the controls.

NFPA 79 - 9.1 - Control Circuits

1. “Control transformers shall be used for supplying the control circuits.”
2. “Transformers shall not be required if the supply voltage does not exceed 120 VAC.”
3. “The VAC for control circuits shall not exceed 120 VAC single phase.”
4. “Control circuits shall be provided with overcurrent protection.”

 

[Firebrick43]

ah, you're right....I'm new at wiring contactors and just realized A1 & A2 is the control....they're available in 120v AC though no?. I figured this schematic was the 'simplest' I could get away with and do it correctly. If I'm ditching the spindle control board feed do I need an 8 pole contactor?

I think w/flood coolant being a possibility, 24 seemed sensible too.

the one in question:

3TH8262-0AK6 Has been discontinued on the siemens portal. I absolutely despise siemens for their "life cycle" shenanigans. ​

Looks like this one is the replacement in 120v

Siemens SiePortal

sieportal.siemens.com

 

[ching0n]

Looks like the Industrial machinery standard, NFPA 79 still allows 120v ac max at the controls.

NFPA 79 - 9.1 - Control Circuits

1. “Control transformers shall be used for supplying the control circuits.”
2. “Transformers shall not be required if the supply voltage does not exceed 120 VAC.”
3. “The VAC for control circuits shall not exceed 120 VAC single phase.”
4. “Control circuits shall be provided with overcurrent protection.”

hmmm, it's possible that this unit expecting 220V elsewhere would require a lower voltage for other locales & commonizing hardware is less expensive? Do you know if the rule changes for 'wet location' due to flood coolant?

 

[American Locomotive]

24v controls are standard, and 24v relays and contactors are super common, that's why they went with it.

They have it setup this way so the e-stop cuts the power to just about everything. It's effectively a power switch.

Also it's just generally good practice to have controls voltage isolated.

 

[Firebrick43]

hmmm, it's possible that this unit expecting 220V elsewhere would require a lower voltage for other locales & commonizing hardware is less expensive?

NFPA 79 is an American standard, not code. But if you want to sell to a company in the US it typically is required to be built to those standards. Or I should say insurance and osha are going to look at those standards so companies will only accept equipment to those standards.

Do you know if the rule changes for 'wet location' due to flood coolant?

Voltage is not affected, but the enclosures and wiring conduits that the controls are located in are affected. NFPA 79 directs the builder to the NEMA 250 document.

Nema 1 enclosures are typical for falling dirt

Nema 2 for dripping liquids

Nema 3 is indoors/outdoors with rain and snow

Nema 4 is hose directed water which is what is typically required for flood coolant systems or wash down areas.

There are others, here is a list.

https://cdn.emotorsdirect.ca/knowledge-center/NEMA%20250%20Enclosure%20Types.pdf

Wiring needs to be either fluid proof cable with compression glands where it enters the enclosure or a flexible conduit like sealtite.

You really should use 24 v

 

[micromind]

Looks like the Industrial machinery standard, NFPA 79 still allows 120v ac max at the controls.

NFPA 79 - 9.1 - Control Circuits

1. “Control transformers shall be used for supplying the control circuits.”
2. “Transformers shall not be required if the supply voltage does not exceed 120 VAC.”
3. “The VAC for control circuits shall not exceed 120 VAC single phase.”
4. “Control circuits shall be provided with overcurrent protection.”

I'm pretty sure I've violated that at least a hundred times in the last 31 years........lol

 

[Steve from Socal]

I think the IEC may require 'safe intrinsic voltage' under 50 volts? The hall effect sensor/speed display are 24 v, contactor same thing.

 

[Steve from Socal]

I'm pretty sure I've violated that at least a hundred times in the last 31 years........lol

I have line voltage controls on several machines at 480.

 

[Firebrick43]

I think the IEC may require 'safe intrinsic voltage' under 50 volts? The hall effect sensor/speed display are 24 v, contactor same thing.

I don't see an actual requirement to be under in the IEC but there are vastly different requirements if the volts is Extra Low Voltage. They define ELV as 50v AC or 120V DC and lower.

 

[ching0n]

NFPA 79 is an American standard, not code. But if you want to sell to a company in the US it typically is required to be built to those standards. Or I should say insurance and osha are going to look at those standards so companies will only accept equipment to those standards.

Voltage is not affected, but the enclosures and wiring conduits that the controls are located in are affected. NFPA 79 directs the builder to the NEMA 250 document.

Nema 1 enclosures are typical for falling dirt

Nema 2 for dripping liquids

Nema 3 is indoors/outdoors with rain and snow

Nema 4 is hose directed water which is what is typically required for flood coolant systems or wash down areas.

There are others, here is a list.

https://cdn.emotorsdirect.ca/knowledge-center/NEMA%20250%20Enclosure%20Types.pdf

Wiring needs to be either fluid proof cable with compression glands where it enters the enclosure or a flexible conduit like sealtite.

You really should use 24 v

Can you think of a reason of going w/a step down instead of a din rail 24DC PSU? Looks about the same cost wise w/o the weight/size penalty. Nevermind, I'm thinking DC not AC.

 

[Firebrick43]

Can you think of a reason of going w/a step down instead of a din rail 24DC PSU? Looks about the same cost wise w/o the weight/size penalty. Nevermind, I'm thinking DC not AC.

Almost all the CNC and automation cells I worked on used DIN rail 24v power supplies. My personal stuff does as well.

Surprisingly our luck with the inexpensive Meanwell power supplies were better than the siemens. Such as an EDR-120-24.

 

[mm08822]

Seems like a lot of wiring for only a few functions. Start/Stop, fwd/rev, and speed control. All that can be done directly with the inputs of the vfd.

Exactly, all the OP needs is what is circled in red.....

 

[mm08822]

The 10V AC output/input is for the remote potentiometer being fed by/to the VFD. By controls I meant the on/off/e-stop/fwd/rev switches, sorry I didn't clarify. I think you may be correct about the spindle speed control board/display though....I'm not using those so might be able to ditch that side.

It's 0-10VDC typically for speed pots. This drive sources its own 24vdc for for/rev, stop/start and other programmable inputs. It was not used as there are too many other coils/loads in the enclosure.

 

[mm08822]

One possibility is that the amount of current on the VFD 24DC controls is small enough that, odd as it may sound, it won't work with pushbutton contacts the have been used with higher currents.

There's not enough energy to blow the contacts clean and even the slightest amount of contamination will cause a failure.

24AC controlling a relay that has bifurcated gold contacts will solve the problem. The gold contacts can handle very low current.

Signal level contact blocks are available for this purpose, but cost more. (Grizzly from China is all about saving $$$).

 

[mm08822]

They did it for the contactor, which is connected to the Estop switch and kills all the motors, not just the spindle that the VFD is hooked up to. And they have the switches hooked up correctly.

Not really sure why the fan couldn't stay on but the way they did wire it is probably about as safe as it can be, if we ignore the lack of craftsmanship in wiring it.

This is how most industrial equipment would be wired, at least schematically. Most of the time they don't kill power(just send the drive into e stop mode) to the VFD itself as heavy loads can be braked faster thru the VFD and braking resistors attached to the VFD but this is a little lathe?

I am not sure that 110v control voltage is forbidden but I have not seen a new machine with it in 20 years. All the stuff I worked on that was 110v control voltage was 1980 and prior build. And when we recontrolled them it was changed to 24v dc. That is the standard. You don't need to worry about shock below 50v DC

The fan could have stayed on, why not keep cooling the enclosure right? I think b/c they daisy-chained off of the contactor they were out of terminals so the next place to pick up 120vac was at the drive input. ($)

DBR's cost money, take up space and make heat, so just drop the input side.

I still remember NEMA coils with 600vac rating!!! Yes, on any decent industrial machine today, 24vdc is the norm.

 

[mm08822]

Looks like the Industrial machinery standard, NFPA 79 still allows 120v ac max at the controls.

NFPA 79 - 9.1 - Control Circuits

1. “Control transformers shall be used for supplying the control circuits.”
2. “Transformers shall not be required if the supply voltage does not exceed 120 VAC.”
3. “The VAC for control circuits shall not exceed 120 VAC single phase.”
4. “Control circuits shall be provided with overcurrent protection.”

NFPA 79 is a guideline as it is not enforceable, except for maybe by company engineering standards written into a PO (but that is elective). I'm not knocking it by any means, but this is Grizzly being sold to mom and pop.

 

[mm08822]

Can you think of a reason of going w/a step down instead of a din rail 24DC PSU? Looks about the same cost wise w/o the weight/size penalty. Nevermind, I'm thinking DC not AC.

If they could get a ps with a 120/240vac input and all loads at 24vdc, then it could work. The fan could easily be bumped to 24vdc.

You can probably avoid 90% of this baggage using an IP65 rated vfd. Power in, motor out wiring at a minimum. On/off, direction, and speed could be from integral keypad or hard-wire to separate devices if keypad too tedious.

 

[Firebrick43]

NFPA 79 is a guideline as it is not enforceable, except for maybe by company engineering standards written into a PO (but that is elective). I'm not knocking it by any means, but this is Grizzly being sold to mom and pop.

I have seen 1 grizzly and two jet lathes in fortune 500 factories. Also OSHA will cite NFPA 79

 

[mm08822]

I have seen 1 grizzly and two jet lathes in fortune 500 factories.

Buyer beware. If the safety rep is happy and equipment performance is acceptable for the expected tasks, then go with it.

 

[Firebrick43]

Buyer beware. If the safety rep is happy and equipment performance is acceptable for the expected tasks, then go with it.

I know. The grizzly was being used basically as a polishing machine for cam lobes. Good job for it and who cares if it was destroyed by the abrasive grit over time.

The Jets were very actually not too bad. The were bought in 2020 and were Jets most decked out 13" models. They were used for making cast iron repair sleeves and general rework. The variable speed and foot brakes plus the lay out of the controls was very acceptable. They really liked them compared to the ww2 vintage loge and shipley they replaced, although they were in no way capable of the cuts the old beast could take. Just much more ergonomic and handy.

 

[Firebrick43]

NFPA 79 is a guideline as it is not enforceable, except for maybe by company engineering standards written into a PO (but that is elective). I'm not knocking it by any means, but this is Grizzly being sold to mom and pop.

yea, I laid that out in post 14

 

[ching0n]

I know. The grizzly was being used basically as a polishing machine for cam lobes. Good job for it and who cares if it was destroyed by the abrasive grit over time.

The Jets were very actually not too bad. The were bought in 2020 and were Jets most decked out 13" models. They were used for making cast iron repair sleeves and general rework. The variable speed and foot brakes plus the lay out of the controls was very acceptable. They really liked them compared to the ww2 vintage loge and shipley they replaced, although they were in no way capable of the cuts the old beast could take. Just much more ergonomic and handy.

here's a precision Matthews. Looks same-ish: