# 2017 NEC 555, minimizing gfi tripping



## class c (Aug 16, 2016)

John Valdez and any others who want to jump in,

I install surface water pumping systems on Texas lakes using multistage submersible downhole pumps in the water, sometimes hundreds of linear feet out in the lake. These pumps were previously the domain of water well drillers, whom all drillers I have contacted despise gfi's and NEVER install gfi's or gfci's for these type pumps. 

Year 2017 is closing fast and the NEC has new rules (555) that require 30 ma gfi protection on the electrical feeds to even private non commercial docks. I am trying to engineer/design a reliable system that does not nuisance trip - - or trips as little as possible when used with gfi's. Pump industry professionals have stated emphatically that it will NEVER be done with VFD driven pumps, for one, the AC -DC -AC conversion of the VFD completely stops the gfi from monitoring properly the pump and pump cable wiring.

Fortunately I only use the old fashioned single phase 240 volt 60 HZ motors with simple control boxes - - although some say there is still a substantial "pulse" when both the start and run windings fire to start the motors.

I have consulted some electrical engineers who gave me a whole range of suggestions:

1) Drive a new ground rod closer to the water's edge - - - more certain ground.

2) One engineer said: "measure the impedance of the different HP motors you intend to use and then the impedance of the length of pump cable you intend to use. Balance the cable impedance against the motor impedance (but did not tell me how to do that).

Another said:" The motor is an inductor, so to “cancel out” its inductive reactance, you need an equal capacitive reactance.
The goal is to have a pure resistive impedance from end to end, with any reactance impedances canceling one another out. This minimizes high frequency waves reflecting (bouncing) from end to end of the wiring (the transmission line). It might be that current peaks from mis-matched impedances could be peaking high enough to set off the GFI. The current is all there in the wires, but the instantaneous phase difference makes it seem like a large unbalance.

Do I understand correctly that 60 HZ power is a low Z situation as opposed to VFI's which are typically high freq, high Z ? I am wondering whether a line reactor on the input of my standard control box to cushion the gfi is useful versus load reactor on the downstream side of the pump control box towards the pump - - - to cushion any spikes from start up of the motor is useful ? Some of our runs out into the water to reach the pumps are like 300 feet of pump cable, but remember, we are NOT using VFD's.

As we know, inductors resist current change and thus smooth current ripple, capacitors smooth voltage ripple. Inductors are put inline to filter electrical noise. Caps are placed in parallel to shunt noise to ground. Both can cause a phase shift between voltage and current, but they do so in opposite directions so the effect cancels out. Another engineer suggested that since I have two hot legs in my 240V design, anything which caused an imbalance btween those two hot legs would cause nuisance tripping, others said since the gfi only measures hot to neutral, imbalance between the two hot legs themselves would not cause nuisance tripping.

Another engineer suggested using a zero-crossing detection type solid state relay to energize the pump control box sending electricity to the pump, He claimed those type relays greatly minimize spikes, but I wonder about how much time delay from time SSR clamps and energy travels through the pump control box circuits and then the 60Hz waveform finally gets to the motor . . .

I intend to try to use the newer class C gfi's with 20 or 30 ma trip and ground continuity checking, although there are too few manufacturers in that realm yet (Bender and Littlefuse so far), so prices are ridiculously high, minimum $800 contractor cost, a bit tough for a private property owner to swallow, but then human life is priceless.


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## class c (Aug 16, 2016)

Excuse my mistake, I meant Valdes


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## JRaef (Mar 23, 2009)

Several issues:

1) GFCI and GFP/GFPE are not the same. GFCI is 5mA trip for Class A (bathrooms, kitchens, outdoor) limited to 125V, 20A and below if it is a plug-in receptacle, or anything in a pool or spa (or carnival equipment). There have been complaints about some electronically controlled motor systems not playing well with GFCIs, I believe it has to do with "common mode noise" being misinterpreted by the GFCI circuitry as ground current. Filtering with an isolation transformer almost always works, sometimes just a reactor works, it depends on the GFCI.

2) 30mA trips and up are considered GFPE (Ground Fault Protection for Equipment). That is NOT known to be an issue for VFDs and other power electronic systems unless maybe there is an issue the installer was unaware of. 30mA is widely required in the rest of the world as "personnel protection", just not here. LOTS of VFDs all over the world are running just fine behind 30mA GFPE devices.

3) Art. 555 for boat docks and such calls for 100mA GFPE, not 30mA. I've heard, though not directly from anyone with any authority, that there is a change coming for lowering that to 30mA. If it happens in the 2017 code, most of us will not have to deal with it until our state adopts it, usually 2-4 years later. Here in CA we are still on the 2011 code... 

4) SSRs are not going to do anything for you. Zero cross is not the issue, and they come with more problems than they solve. RAMPING via a soft start (which is not zero cross) can reduce the starting current surge by stretching it out over a longer period, but is not a good idea with most single phase motors. Again, more harm than good.

I think before you over react, try them out. MOST people have no issues at all with standard motors behind GFCIs. I have a 60A Class A GFCI on my hot tub that has 2 single phase motors on it, the ONLY time it has ever tripped is when the heating element insulation failed, meaning it did EXACTLY what it was supposed to do. I have never heard of widespread issues of standard motors behind GFPE devices.

One thing that is going on however is that there are some pumps for pools and such that have built-in VFDs or use what is called an "ECM" (Electronically Commutated Motor), basically a permanent magnet motor that has a built-in VFD like device for it. Those are NOT "standard" full voltage motors, and people don't realize it because they don't see a separate box that looks like a VFD. So when those get connected to some GFCIs, they cause nuisance tripping. Stay away from those and you should be fine.


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## chicken steve (Mar 22, 2011)

I don't have a '17 as yet, but i did sit in iaei class last month where Jeff Sargent informed us all commercial receptacle outlets under 100A shall be class A gfci protected 

there was audible groans in the room.....

~CS~


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## class c (Aug 16, 2016)

*minimizing . . . .*

1) Yes, I was aware of everything except the common mode noise as a cause. It was also pointed out to me some of the disadvantages of an isolation mode transformer.

2) As per class C devices, if you have in place a confirmed and monitored ground of same size as other conductors, the ground acts as the main attraction for stray current so there is much less chance of needing "let-go" capability, and the ventricular fillibration is covered by the higher 20 am or 30 ma (like the European and other countries values). Also, a victim getting in between the hot to neutral conductors could still occur with a 5 ma GFCI monitoring a situation and not trip it.

3) As I stated in my original post, Year 2017 is closing fast and the NEC has new rules (555) that require 30 ma gfi protection on the electrical feeds to even *private* non commercial docks. Right now it is 100 ma for commercial, but the 2017 revision is 30 ma - - including non-commercial (is that sneaky language ? Why not just come out and state private ?). I certainly agree on the lag time before the the local authorities adopt it.

4) I now looking at RC snubbers to "soften" the motor starts, I have read some folks are seeing positive results, and the cost is very minimal.

Glad you are having great results with your hot tub, but have a chat with any well driller and you'll see what I mean about GFI's and GFCI's, Goulds pumps states in their literature "don't even try". Maybe you should try hooking up a 5 ma GFI to a submersible multistage pump that's 300 feet out in a lake sometime and see what you get.

Seems if you're pump system is on a 30 amps or over circuit, and not a plug in device (hard wired), you should be be able to argue the code to inspectors.

Was not aware of the ECM motor problems, thanks for bringing it to my attention. I'll try to keep it in my knowledge base.


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