Need some GFCI help..instant tripping on power up

[VE7 Kilohertz]

Hi Gang,

Just installed a new to me hot tub in ex. cond. and have added a dedicated sub panel with 8/3 wire and a 40A GFI breaker. Upon application of power from the main panel in the house, the GFCI trips instantly. I went through and disconnected the heater, no change, the pump, no change, the ozonator, no change, still trips. Decided to measure the blk/red wires to ground and neutral to see if I could see any leakage (resistance with power off) and what I found was 13 ohms from blk to wht wires, across one leg of the 120VAC. Probed around on the cct brd and found that the little power transformer that supplies 12 and 24VDC to the ccts, relays etc, gets it's primary power from 120VAC, blk and wht wires. Now when I pull the plug for this transformer, and reconnect the pump heater etc. the breaker istays on. My thought is that the little transformer is only drawing from one side of the 240VAC line and thus causing an imbalance or current flow in the neutral. But how could the tub work with a GFCI if this is wired like this. Am I thinking correctly? I also removed the xmfr and floated it on a piece of wood, disconnected the secondary, and with only the primary connected (20VA xfmr) is STILL trips the breaker.   There must be something I'm missing here.  Maybe I don't know how GFI's work.   I thought they measured current in the neutral line, but if hot tubs have 120V loads like blowers and control ccts, causing an imbalance on the neutral, as well as the big ones like pump and heater, which have balanced 240VAC loads, how do they work?


I have re-checked all of the wiring, and the neutral floats all the way to the tub, only the ground is grounded and only at the service entrance.

Arg! Help please.

Thanks

Paul

[WA1GFZ]

I don't know how a 240v GFI works but maybe you need to install a 240 to 120 transformer to get it going. Sounds like it senses any neutral current to get a trip. 
Heck you might get away with a power resistor in series with the primary and throw it across the 240 vac line.

[KF1Z]

I bet this will help...

http://www.angelfire.com/mi2/hottubs/electrical.html

[John K5PRO]

I thought most modern 240V GFIs sense difference current between the two hot legs, and assume that if there is a difference, it must be neutral or ground current, and trip off when it exceeds a level. I had a GFI fail on my hot tub, after about 5 years. It failed high resistance on one leg, so that things appeared to be OK, but when the heater ran, it was not hot enough. Through substitution of everything, including controller, heaters and thermistor, the service man gave up. It was still under warranty. Then I replaced the GFCI breaker (a GE) and that fixed it.

[KB2WIG]

I've found that the following "forum(s)' to be very helpfull fer  'lectrical stuf

"http://forums.mikeholt.com/showthread.php?t=86601


klc

[K4TLJ]

I've found that the following "forum(s)' to be very helpfull fer  'lectrical stuf

"http://forums.mikeholt.com/showthread.php?t=86601


klc

But that forum is for licensed electricians. They tend to frown on questions from unlicensed folks from my experience.

[n2bc]

Hi Paul,   I have two two-pole GFCIs which feed subbanels which in turn feed individual 120V devices.  Clearly in this case the load between the two hot
conductors is not equal.

I don't know how the darn things work, but equal current flow between the A and B sides is not part of the equation.   In any event, I am not getting GFCI trips caused by unequal A/B current.

By the way, one of the sub panels is a feed into my garage and it has tripped when I've acciidently doused a motor when hosing out the garage floor.

There could be another factor... you guys use metric electrons don't ya???

73, Bill   N2BC


Update:  Been thinkin' about this....   you didn't happen to wire-nut the neutral going out to the hottub to the white pigtail on the breaker did you???

Good pix of typical 2-pole breaker setup here:  http://www.rhtubs.com/seimens-GFCI.htm

[KB2WIG]

 " But that forum is for licensed electricians. They tend to frown on questions from unlicensed folks from my experience. "

Yes, you are right....  From the site,

"
Do-it-yourselfers
This is not a site for do-it-yourselfers.
This Forum is intended to assist professional electricians, inspectors, engineers, and other members of the electrical industry in the performance of their job-related tasks. However, if you are not an electrician or an electrical contractor, then we are not permitted to help you perform your own electrical installation work.
The stated purpose of the formOther electrically related individuals "

Also posted,

"
This site is designed for:

Contractors
Electricians
Engineers
Inspectors
Instructors
Other electrically related individuals    "

The information in the forums is usefull, and like AMfone, ya don't have to be a member to read.

On another note, Welcome aboard Terry....... 

klc

[w4bfs]

the following discussion is an extrapolation from 120 Volt GFCI operation and may or MAY NOT be true...

The GFCI is looking for a balance of supply and return currents by using a torroidal current transformer that is multifilar wound.  As long as the currents balance to less than 7 mA, the GFCI will not trip.

 This is easy to understand in the 120 V breaker as the current transformation is done with the one 'hot' and neutral. Any current that diverts to ground will upset the balance.  This is why GFCI's can be used in old 2 wire systems and still give ground fault protection

Extend the idea to 240 V operation by trifilar winding the ct.  Any current entering by one 'hot' leg must either leave by the other 'hot' or neutral to maintain balance.  Anything else would be a ground fault.

This is one of the reasons why the branch circuit neutrals are attached to ground ONLY at the main load center / service entrance .

73   John

[VE7 Kilohertz]

Hi Guys,

Thanks for the thoughts, links etc. They have confirmed I have the breaker setup correctly. Sounds like it may be a flakey GFCI breaker. I will try a new one and see if that fixes it...if not...mmmm back to the drawing board.

I wonder if having ground rods outside the ham shack, 50 feet from the main panel, could be causing ground loops or some issues?  I also have power going to the shop with another ground rod out at that panel. The tub is sitting on a fir deck, 3 feet off the ground.

Cheers

Paul

[Steve - WB3HUZ]

Are all the ground rods tied directly together with large size wire?

[WA1GFZ]

Also for good lightning performance all grounds should be single point grounded back to the panel so there is no voltage offset if one gets nailed.

[VE7 Kilohertz]

Ground rods...

Nope, the one outside the shack is tied to the big broadcast TX, which then goes back to the panel through the #10/3 wire. The one outside the shop goes to the main house panel thru the #4/3 service wire feeding the shop.

Re: the GFCI, I bypassed my Federal Pioneer SPA box and put a new Square D 40A GFCI in the sub panel in the basement...voila! It works. Nothing wrong with my wiring or the tub. It was a flakey breaker. Bloody hell. 

Well, I always enjoy learning about new things and GFCI's are a good thing to know about.

Thanks for all the help and links.

Cheers

Paul

[W1RKW]

What happens if the neutral and ground wires are of unequal lengths electrically or even physically? Would that matter in terms of ground loops?  Or even different wire sizes in circuits....

[WA1GFZ]

Bob there should be no current on the safety ground of the GFI should trip.
It senses by sending the hot and return through a transformer reverse phase to cancel flux. Any imbalance and there is energy to trip the breaker. I think someone said 7 ma is the trip point.

[Steve - WB3HUZ]

There would have to be a big difference in length to matter. The wavelength at 60 Hz is something like 3000 miles.

What happens if the neutral and ground wires are of unequal lengths electrically or even physically? Would that matter in terms of ground loops?  Or even different wire sizes in circuits....

[WA2TTP Steve]

Maybe this will help. I got this info from the site linked below.
I think the part about GFCI's for hybrid loads may be the root of your problem.

http://www.poolandspa.com/page797.htm



Ground Fault Circuit :
Interruption Protection   
(GFCI)     GFCI protection is necessary in case anything electrical should allow electricity to leak to grounded metal in connection with the spa. This is especially possible if after years of use a heater element should rupture and the ground wire (that may or may not have been originally connected) should happen to become disconnected. A GFCI will sense this leakage and shut the voltage to the power pack oft.
As of January 1, 1994, all equipment packs used with a spa or hot tub must be protected by a Class A ground fault circuit interrupter. This is called for in the N.E.C. code book in paragraph 680-42. If the equipment has a GFCI built into it,that GFCI may only protect certain components such as the blower, light ozonator, and sometimes the pump. The GFCI may not provide full protection, especially if the unit is wired for 240V service. To be sure, have a qualified electrician study the wiring diagram that came with your unit (or the manufacturer of the unit you are working on) for verification.

Keep in mind that when buying a 240 GFCI for an installation, be sure to get one that has neutral protection. The 60A Square D GFCI does not have neutral protection and therefore cannot be used on a hybrid equipment system. (Hybrid means the unit contains both 240V and 120V components.)

NOTE: Any GFCI protecting a circuit should be tested periodically to insure proper operating protection. If it fails to operate properly, it must be replaced.
 
240V Circuit Breaker :
Installation      There are two easily installed properly rated 240 volt GFCI breakers on the market today (as of the time this page was written). They are the Square D model QO 250GFI and the ITE Siemens model QF250, each rated for up to 50 amps. The square D 60 Amp GFCI can not be used with our equipment because it does not have load neutral protection.
Most people who install the Square D GFCI breaker do not follow the instructions accompanying it. A common mistake is made by connecting their load neutral (from the equipment), the large white pigtail on the GFCI, and the power supply neutral to the connection block on the mounting bracket. The instructions show where the load neutral is supposed to attach to the GFCI. Before suspecting a pack malfunction, check the installation of this device (when used) and make sure it was installed correctly.

The connection points for the pack on the Siemens GFCI are more obvious, but again, make sure that only the load neutral is connected where indicated and that the white pigtail is only connected to the line service neutral.
 
73,
Steve
WA2TTP

[WA1GFZ]

HUZ,
Lightning saw WF 3 has a frequency component up to 10 MHz. and maybe a little higher. WF 2 has a 100 ns rise time. (RTCA DO 160) It ispretty easy to generate voltage offsets if the ground system isn't referenced back to one point.

[Steve - WB3HUZ]

True. But if the various wires all leading to a single point ground are slighltly different in length, I don't think it will matter. The important part is that they all lead to a single point, as you noted.  In long runs the inductance of the wire will tamp down the higher freq components anyway. With multiple ground points, strike energy can back fed up one of the grounds and blast eqiupment on that leg.

HUZ,
Lightning saw WF 3 has a frequency component up to 10 MHz. and maybe a little higher. WF 2 has a 100 ns rise time. (RTCA DO 160) It ispretty easy to generate voltage offsets if the ground system isn't referenced back to one point.

[WA1GFZ]

That is why in your earlier post tie all grounds in a grid to limit offset voltages. You want everything inside the house referenced to the single point so there are no offsets generated in the house. Outside bond everything to everything back to the single point.
Most of us are guilty of two ground systems shack and RF. Not a good idea for lightning.

[Steve - WB3HUZ]

Yep. Many hams do it. I did for years, a separate ground for the shack. Then I took a grounding course and thought to myself "OH crap!" Those grounds got tied together after that.