Three Phase GFCI?

[chrisplusian]

Working on a motor which will be on a floating deck in the middle of an 80 foot diameter dunnage pond. Supply voltage is 480 via VFD and looking at the VFD literature it has ground fault detection built in when there is a difference in current detected at 25% of the drives rated amperage. For this application that would be a 13 amp difference. Which made me think... I should look to see if any other ground fault protection needs to be provided based on 2020 NEC. Both 682.15, and 210.8(B) only carry requirements for single phase and I had to stop and ask why? I know there are GFCI for 208V VFD systems, and while I realize a Class A GFCI has a maximum voltage limitation of 240V I still can't understand why there would not be a requirement for a 480V system running a motor in the middle of a pond to have ground fault protection per code. Can someone help me understand why there seeems to be no requirement for 3 phase circuits?

 

[Jraef]

Lol… answers to “why” questions and the NEC are enigmatic…

It USED TO BE that GFCIs were intended to be for residential use on circuits that the vast majority of people would encounter every day, like in bathrooms, kitchens, pools, spas and outdoor outlets. But “mission creep” has moved them into more and more places to the point where we are now EXPECTING them to be anywhere that water is present. I don’t think that mission creep has moved into 3 phase applications, at least not yet, probably because they tend to be hard wired, and exist in workplaces that, unlike a residence, are supposed to have electrical safety programs.

 

[chrisplusian]

Lol… answers to “why” questions and the NEC are enigmatic…

It USED TO BE that GFCIs were intended to be for residential use on circuits that the vast majority of people would encounter every day, like in bathrooms, kitchens, pools, spas and outdoor outlets. But “mission creep” has moved them into more and more places to the point where we are now EXPECTING them to be anywhere that water is present. I don’t think that mission creep has moved into 3 phase applications, at least not yet, probably because they tend to be hard wired, and exist in workplaces that, unlike a residence, are supposed to have electrical safety programs.

Yeah I get that. I looked back at my code books from 2002 forward trying to track how we got to where we are, and what we used to do, and it wasn't obvious. I have always approached code from a "why" perspective because that is how I understand things.

 

[suemarkp]

Can someone help me understand why there seeems to be no requirement for 3 phase circuits?

It is creeping in. There is a 3 phase requirement in the 2023 210.8(B) section:
All 125-volt through 250-volt receptacles supplied by single-phase branch circuits rated 150 volts or less to ground, 50 amperes or less, and all receptacles supplied by three-phase branch circuits rated 150 volts or less to ground, 100 amperes or less, installed in the following locations shall be provided with GFCI protection:

Doesn't cover 480V 3 phase, but give them time...

 

[don_resqcapt19]

Lol… answers to “why” questions and the NEC are enigmatic…

It USED TO BE that GFCIs were intended to be for residential use on circuits that the vast majority of people would encounter every day, like in bathrooms, kitchens, pools, spas and outdoor outlets. But “mission creep” has moved them into more and more places to the point where we are now EXPECTING them to be anywhere that water is present. I don’t think that mission creep has moved into 3 phase applications, at least not yet, probably because they tend to be hard wired, and exist in workplaces that, unlike a residence, are supposed to have electrical safety programs.

It is expanding to 3 phase equipment.

210.8(B) (from 2023 code) (B) Other Than Dwelling Units.
All 125-volt through 250-volt receptacles supplied by single-phase branch circuits rated 150 volts or less to ground, 50 amperes or less, and all receptacles supplied by three-phase branch circuits rated 150 volts or less to ground, 100 amperes or less, installed in the following locations shall be provided with GFCI protection: ...
(D) Specific Appliances.
GFCI protection shall be provided for the branch circuit or outlet supplying the following appliances rated 150 volts or less to ground and 60 amperes or less, single- or 3-phase:

While (B) only applies to receptacles, (D) applies to outlets which includes hard wired equipment.
Article 680 has added rules that require Special Purpose GFCIs for equipment up to 480 volts.

680.5 (C) Above 150 Volts to Ground.
Where required in this article, ground-fault protection of receptacles and outlets on branch circuits operating at voltages above 150 volts to ground, not exceeding 480 volts phase-to-phase, single- or 3-phase, shall be provided with SPGFCI protection not to exceed 20-mA ground-fault trip current.[/quot]
Other rules in 680 specify when you need SPGFCI, with one example being a pool pump motor that is supplied by a circuit with a voltage to ground that exceeds 150 volts.

 

[aquatic1]

680.5 (C) Above 150 Volts to Ground.
Where required in this article, ground-fault protection of receptacles and outlets on branch circuits operating at voltages above 150 volts to ground, not exceeding 480 volts phase-to-phase, single- or 3-phase, shall be provided with SPGFCI protection not to exceed 20-mA ground-fault trip current.[/quot]
Other rules in 680 specify when you need SPGFCI, with one example being a pool pump motor that is supplied by a circuit with a voltage to ground that exceeds 150 volts.

This is currently causing problems in the recreational aquatics industry:

1. High cost of 480VAC 3 phase SPGFCI devices.
2. Low availability of 480VAC 3 phase SPGFCI devices.
3. Additional equipment room space required to mount these SPGFCI devices. (As far as I can tell, they do not come built into a breaker).
4. Nuisance tripping of SPGFCI by many VFDs. (Requires careful selection of VFD manufacturer and can force owners not to use their preferred brand of VFD. Additionally VFD manufacturers do not typically document their performance on a GFI protected circuit.)

Curious of any thoughts or suggestions on these challenges. Is this rule overly restrictive or is it demonstrably justified in its protection of people and property?

 

[garbo]

PM'ed hundreds of VFD'S & Troubleshoot and repaired them. I see two problems if you wanted to use off the shelves three phase 480 volt GFCI protection. If you were to install it on the line side of a VFD do not think it would pick up ground faults because the 480 volts is feed to a full wave rectifiers creating a two wire 660 Volt DC buss voltage ( that is filtered with capacitors ) that feed the IGBT'S that produce a chopped output voltage & frequency. Believe Modern drives have switching frequencies at least 5,000 times a second. Doubt if any off the off shelve 480 volt three phase GFCI'S would work on VFD output due to low voltage & frequency while operating at low speeds. A typical VFD running at 30 Hertz ( halve speed ) the voltage would only be 240 volts. Several times a month I would get a call for one of the 500 VFD"S tripping out on what some drives display as Earth fault. At least 85% of the time they was no grounds when I meggered the motor. Would pencil in fault & date. Might be two years later same drive produced same false fault code. Drive techs told me drive manufacturers use some kind of calculations to show ground faults. We had 8 outdoor 75 HP exhaust fans that would shut down due to earth fault. Removed motor leads and rang out a few of the motors and always meggered great ( over 500 million ohms to ground using a 1,000 volt megger ). Finally asked our great drive tech. He told me for a short period drive company received faulty control board ribbon cable that produced these false earth fault shutdowns. Even though these outdoor drives were over 5 years old they were covered under warranty.