Residual Current Circuit Breakers (RCCBÆs) - Problem 3

[claver]

We have a stange problem involving RCCB. We have 6 battery chargers connected to a 3ph supply – 240V line to line (2 Chargers on phase 1, 2 chargers on phase 2 and 2 chargers on phase 3 .. All chargers are 240 so we have had to connect them line to line to get the correct voltage, Each charger can pull 3.5kW … We use a 50A 3ph supply.
We have a 30mA RCCB on each phase (

http://www.hager.com.sg/menu/produc...ircuit-breakers---rccbs---elcbs/800-1483.htm)

. The equipment has been working fine in New York. We then move the equipment to Chicago and we now have constant problems with 2 RCCB’s tripping almost immediately. The chargers and cabling is fine, no damage …

Is it possible that the supply (which is obviously upstream of the RCCB’s) can have any influence on a RCCB ?? The only thing that has changed is the electrical supply …from one geographical location to another … My understanding of RCCB’s is that any problem before (upstream) the RCCB’s is irrelevant … it only measures what is downstream ….

Would much appreciate if anyone could put some light on this …

 

[itsmoked]

No chance you're now on 208V?

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[claver]

Nope .. I have been told we have a good 230 - 240 supply ... Even if it was 208V .. (the chargers work down to 200V)the RCCB should still work ok ...

 

[itsmoked]

Can you tell us about the chargers? Switching supplies? Or just transformer/rectifiers?

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[claver]

They are compact switch mode chargers ... Used frequently in Europe ... We have never had RCCD problems with them before. I can not believe 4 have failed in "transport" ... ??

 

[itsmoked]

I would agree they haven't. But as you see something has changed.

Switcher type can have capacitive coupling issues that allow leakage that the RCCDs consider ground faults.

It will likely be something subtle.

Do they run for a while, and then trip, or just flat trip immediately?

Trip when not running?

This is WYE power? There is a neutral you're not using?

Was the power Delta at the prior location?

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[claver]

They may run for 1/2 hour ...sometime just 5 min ... If the charger is off ... no trip.

I agree with the capacitive coupling issue with this type of charger. But as I say 4 failing at the same time ??
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We are not using the neutral.

Both installations are supposed to be the same - Neutral not used

Appreciate you comments...

 

[itsmoked]

How long was the wire run from the RCCBs to the chargers in NY?

How long are the runs now?

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[waross]

A couple of suggestions.
How is your power quality? If you have a lot more harmonic distortion in the new location that may be affecting the trip elements.

In North America, 240 volt three phase systems are generally delta fed.
The delta may be corner grounded, which will put two phases at 240 volts to ground. The leakage to ground will be higher.
The delta may have be a 4 wire 120/240 single phase-240 volt three phase. If so, the code requires the center point of the 120/240 volt transformer to be grounded. This results in two phases at 120 volts to ground and one "Wild" phase at 208 volts to ground.
The delta may have an artificial neutral to provide a symetrical grounding point. If so, all three phases will have 139 volts to ground.
You may want to see if you can identify the system types in use at both locations.
When the voltages to ground are equal, the 60Hz leakages to ground from each phase tend to cancel rather than returnng through the neutral.
Insulation losses caused by triplen harmonic voltages do not cancel but add on the neutral and pass through the GFI trip unit.
You may want to check that identical GFI breakers are installed at each location.
As Keith says, wire lengths may be significant.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[Kiribanda]

Claver,

If I understood your problem correctly,it seems that

1)The RCCBs were supplied at 240 V 3-phase in NY
2)The RCCBs were supplied at 208 V 3-phase in CHICAGO.

Normally these RCCBs are having an intergal electornic circuit with an amplifier which works on a defined voltage range.It takes its control power from the input line side. So there is a possibility that when you feed a lower input voltage (208 V) to the RCCB, the elctronic circuit may trip due to under voltage and shutdown the unit.

Any comments please.

Kiri

 

[claver]

Thanks for all you comments! I am trying to get to grips with the way the US does it electrical installations.

The cable length from the RCCB to the chargers are the same in both locations. But the equipment is mobile and operate from a extension cable. The length is the about 50ft - 60ft. But the cable is BEFORE the RCCB. The RCCB is mounted on the mobile equipment. It is the RCCB on the equipment that trips. Not in the "building".

The voltage was the same in both locations 240V. That is definite. Waross may have hit on a interesting point. I am also surprised that the cable length may have an influence.

My understanding of the workings of the RCCB that we use is that it compares the current going in each line. If the current is not the same . (The tolerance is 30mA) It assumes that the current must have gone to ground and the unit trips.

We are now moving the equipment to California. Will know next week if we have the same problem at the new location !

Any further comments or suggestions are highly apreciated

Have a good weekend !

 

[gepman]

Cable length (after the RCCB) affects performance due to the capacitance of the cable. Remember capacitors store charge so whatever it is storing does not make it back through the RCCB.

You won't have any problems in California, our electrons, like the weather, are much better behaved.

 

[slavag]

Hi Claver.
I'm not so work with RCCB, but in our area RCCB used in all
LV application exclude UPS connection. Same RCCB ( different companies, SIEMENS, Hager, ABB, MG, etc.) with 30mA range. I never heard about any influence of cable lenght on the RCCB operation.
You are right, priciple of operation of RCCB it's eql. between in and out current, that means problem is possible only into your mobile eq. BUT we assume that your eq are O.K.
What I can recommend:
1. Check leakedge current.
2. Try put with 30mA RCCB in series 50mA and 100mA RCCB and check what will happened.
I'm also not sure if voltages 110V or 208V or 240V can influence on the RCCB operation.
BUT, I think, grounding type of supply (TNC, TNN, TN-C-S)
must be influence on the level of leakedge.
I think, Bill excplained it as well.
Regards.
Slava

 

[dpc]

I'd expect cable length to be a big factor, along with any moisture along the way. Wet cables are prone to more leakage current.

 

[itsmoked]

Hello claver, slavag;
You realize that if you hooked a resistor between the hot and the safety ground wire you would get a current imbalance that if sufficient would reach 30mA and trip the RCCB right? Of course, that's the whole point.

So if you hooked a capacitor up instead of a resistor since this is an AC system you could achieve the same tripped result. Most every AC wiring system has the HOT in close proximity to a safety ground, whether it's a metallic conduit, or the associated safety ground traveling along with the hot. Hence a capacitance/foot(meter).

So, if the wire run after the RCCB gets long enough you will almost always reach 30mA of leakage, sooner, or later. Sooner, if the cable/wiring has higher capacitance, later if it is lower.

We have a lot of conversations here about faulty, flaky, safety circuits for long systems like conveyors where you can't even use AC in the circuit because the capacitance is enough to cause malfunctions.

That's why you have to ask about length.

Now if the RCCBs are on the equipment.. That likely isn't the problem, agreed!

So what does that leave? Hmmm. Not sure. Switchers often have front end filters that can have capacitors to ground. I had a computer with the standard LC filter puck. The ground was not connected to the case of the filter. The capacitors in the filter 'leaked' to the computer chassis. It would nail you if you touched it.

It could be you had higher safety ground resistance before and the equipment's leakage was 29mA(all the time), now here with a lower ground resistance it just tips over the edge. Perhaps you could put an ammeter in the ground return to see just what's happening. Any chance before the equipment was isolated from ground and now it isn't? Like it was on rubber wheels and now it sits on concrete?

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[claver]

I agree that wet cables is possible a real problem.. But again my point about before and after the RCCB still stand... And as the RCCB is after the cable. I can not see the relevence.

I think Bill's coment about the earth (TNC, TNN, TN-C-S) sound to me the most plausible reason for the problem.

Can someone explain the abbreviations please

TNC
TNN
TN-C-S

Thanks

 

[claver]

Keith,
I was typing my reply before I had seen your reply... The equipment is actually on rubber wheels... I will see if I can get our service engineer to check the ground connection with a clamp on current tester. The ground connection is via the extension cable - We use no separate ground spike/rod

The wire installation - After the RCCB is a standard wire harness we have used for a few years here in Europe, and we have not had RCCB trips that we could not explain (water in electrical boxes or loose connections etc.. I can understand)

But this is first time we have had the equipment working in the US ... so I think that it may be an "upstream" problem. Will be very interesting to see if the "electrons" in California is any better..

 

[slavag]

Hi Claver.
Please see attached:
thread238-201637
you will found usefull information.

Keith, I need think about your point, on this moment I haven't any opinion.
Regards.
Slava

 

[slavag]

Oops. After re-reading.
Claver, what do you mean: neutral not used?
Could you please send us some scheme of internal connection.
Regards.
Slava

 

[slavag]

Please see also some example of RCCB connection:
Good Luck in California