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Old 24-04-2014, 23:39   #1
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ELCI and Isolation Transformer

Hi All
I am reworking my AC system and have run into some things that have stumped me. Ive read this thread: Isolating Transformers, The Earth wire connection conundrum
(all 12 pages) and am no further ahead.
The boat is wired for 120V with an inverter/charger
I have a 30A ELCI on the main panel and have purchased a Charles 120/240 ISOG2 isolation transformer to deal with galvanic issues and allow me to connect to 240V power in the future.
I was planning to keep the ELCI at the main panel and put a selector box ahead of the IT (allowing me to switch between 120V or 240V Circuit Breakers) but in looking at the wiring diagram for the Charles ISOG2 I'm supposed to connect secondary earth and neutral together. Doesn't this negate the push to test feature of the ELCI (meaning it wont trip)?
What am I missing
Thanks
Gary
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Old 25-04-2014, 02:48   #2
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ELCI and Isolation Transformer

There should be no connection between the incoming shore earth and the boat protective earth wire. ( in an IT installation ) . The incoming earth can be connected to the electrostatic shield of the IT for a bit of safety if the primary windings fail . ( the elci will catch that anyway.

ABYC and others recommend connecting the case ground of the IT. To the incoming to the shore earth. I personally think that introduces an impressed current path. If you do that ensure the case doesn't touch anything and do moisture path to the hull exists. ( mount it on insulating rubber grommets. ) or better switch to a plastic case



Connecting the secondary side neutral to ships AC protective earth is to allow the secondary side breakers to trip , ie to simulate or spoof an earth fault.

ABYC wants you to reestablish an onboard earth reference , ie by grounding the secondary side earth / neutral connection to seawater. However as discussed in the thread this is a bit of debate about this.

The incoming primary's should be protected by the elci and a breaker ( or a combined unit )

Note for dual voltage support. Normally the primary is switched. The boat remains a fixed designed voltage with one set of secondary side breakers.

You could also fit a whole boat elci to the secondary side for a bit of belt and braces safety, even though it will not do a huge about. It will detect fault currents running back to the secondary neutral via the boats AC protective earth wire. ( the elci is wired on the boat side of the secondary neutral / AC protective earth bond point.

Dave
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Old 25-04-2014, 10:36   #3
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Re: ELCI and Isolation Transformer

Thanks Dave
Everything makes sense so far. I plan to do the 120/240 switching on the primary side. Of course the secondary side will always be 120.
I have only connected the shore earth ground to the shield. Currently the ac and dc grounds are distinct. This morning I hooked up the ELCI on the secondary side. As I expected it doesn't trip when hitting the test button. I don't understand what use it can have over a normal breaker if it won't trip. Putting it on the primary side would only protect the 7 feet of wire plus shore cable. Not a huge use there either. Why are we spending the extra money on these things if we have an isolation transformer?
I know I'm still missing something.
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Old 26-04-2014, 05:11   #4
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Re: ELCI and Isolation Transformer

Quote:
Originally Posted by gpeacock View Post
Thanks Dave
Everything makes sense so far. I plan to do the 120/240 switching on the primary side. Of course the secondary side will always be 120.
I have only connected the shore earth ground to the shield. Currently the ac and dc grounds are distinct. This morning I hooked up the ELCI on the secondary side. As I expected it doesn't trip when hitting the test button. I don't understand what use it can have over a normal breaker if it won't trip. Putting it on the primary side would only protect the 7 feet of wire plus shore cable. Not a huge use there either. Why are we spending the extra money on these things if we have an isolation transformer?
I know I'm still missing something.

Yes on the shore side you are only protecting 7 feet. Personally I would have it do that.

As for the secondary side Have you connected the elci after the common neutral AC ships protective earth wire bond point.

Furthermore on some ELCI a you have to connect the white pigtail line to the neutral point before ( note ) the elci not after.


The test function should work.

By the way. I would not connect AC earth to DC neutral especially with a IT providing safety. ( whatever ABYC says )

Dave
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Old 26-04-2014, 08:56   #5
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Re: ELCI and Isolation Transformer

I went back and re read Dave's post on Isolation transformers and grounding. Im more confused than ever as to what would work best for me. I expect the huge difference of opinions has to do with different countries having different power setups and different standards. To help eliminate any confusion in this post here is a clarification of what I am trying to achieve.
I have a 43 ft sailboat wired for 120V AC
I have an Bluesea 120 V 30A ELCI (breaker and RCD)
I have an old 120V 1.5KVA Xantrex Freedom Inverter/Charger
I just purchased a Charles ISOG2 120/240 Isolation transformer

My reason for buying the IT was twofold. First to protect against Galvanic issues when connected at suspect marinas in Mexico. Secondly to provide the ability to connect to 240 when in countries further away than Mexico.

Before I installed the IT I assumed the master ELCI would protect shore AC and inverter AC. Now that Ive read a million posts on this subject I realize that was incorrect. My inverter/charger has its own 15Amp breaker which feeds a subpanel of breakers. At least all of the subpanel circuits have a GFCI in them.

I wired the Charles IT as described in the manual as follows:
Wire from shore power cord directly to normal 30 Amp breaker then to IT
primary ground only to the shield.
secondary ground and neutral tied at IT also tied to case.

I wired the double pole ELCI as described in the manual as follows:
Hot and Neutral Wire from IT to Line connections
Hot and Neutral Load wires through coil and to House breakers (including Inverter source breaker)
Neutral ELCI pigtail not through coil to House neutral bus.
Ground wire not through coil to House ground bus.

I need this question answered first:
When powered up everything works but pushing the test button on the ELCI does not trip the breaker. WHY? When I get to the boat today I will remove the IT from the system again and push the button to see if it still works.
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Old 26-04-2014, 10:11   #6
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ELCI and Isolation Transformer

The pigtail must be wired BEFORE the neutral goes through the elci.

( I said this before. ) do not connect it to the neutral anywhere AFTER the elci.


The pigtail provides a route for test current to bypass the coil and hence unbalance the elci.

You need to check this. ( I see you said its done but just check it)


Dave
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Old 26-04-2014, 20:05   #7
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Re: ELCI and Isolation Transformer

Dave, thank you so much for clearing up the neutral pigtail issue. I had a preconceived notion in my head and read your previous post the way I wanted to. The ELCI now trips. Feel free to call me stupid.
Im learning lots here. I still have to get through re reading your other post before I decide to float or not float the AC. Now the easy question. If my inverter charger leaks current to DC or my hot water tank shorts and I move the ELCI ahead of the transformer it wont trip correct?
Thanks again for sticking with me through this
Gary
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Old 26-04-2014, 20:27   #8
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Re: ELCI and Isolation Transformer

Quote:
Originally Posted by gpeacock View Post
Dave, thank you so much for clearing up the neutral pigtail issue. I had a preconceived notion in my head and read your previous post the way I wanted to. The ELCI now trips. Feel free to call me stupid.
Im learning lots here. I still have to get through re reading your other post before I decide to float or not float the AC. Now the easy question. If my inverter charger leaks current to DC or my hot water tank shorts and I move the ELCI ahead of the transformer it wont trip correct?
Thanks again for sticking with me through this
Gary

The main thrust of the Earth conundrum thread is the approach to failure mode analysis and how much emphasis you place on specific fault modes. It's turns into a piece of string argument.

With a IT and assuming your charger is on the secondary side, then if you get an AC leak to DC. ( personally this is one of those failures I discount. ) then there is no return path to trip the ELCI. Equally you can't get a shock from that fault mode because you can't insert yourself into the circuit ( well not easily ).

Connecting the secondary side AC earth ( in effect the neutral of the IT) to the DC negative, now provides a fault path and will cause the ELCIs to trip. But this connection also in itself introduces some additional fault modes, such as the risk of using seawater as the IT return.

There no easy answer and different standards bodies have focused on different aspects.

Dave


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Old 26-04-2014, 20:28   #9
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Re: ELCI and Isolation Transformer

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Originally Posted by goboatingnow View Post
The main thrust of the Earth conundrum thread is the approach to failure mode analysis and how much emphasis you place on specific fault modes. It's turns into a piece of string argument.

With a IT and assuming your charger is on the secondary side, then if you get an AC leak to DC. ( personally this is one of those failures I discount. ) then there is no return path to trip the ELCI. Equally you can't get a shock from that fault mode because you can't insert yourself into the circuit ( well not easily ).

Connecting the secondary side AC earth ( in effect the neutral of the IT) to the DC negative, now provides a fault path and will cause the ELCIs to trip. But this connection also in itself introduces some additional fault modes, such as the risk of using seawater as the IT return.

There no easy answer and different standards bodies have focused on different aspects.

Dave


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Old 26-04-2014, 20:35   #10
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Re: ELCI and Isolation Transformer

This UK canal boat site (narrowboats, usually steel hulls) has some helpful information and clearer diagrams than many others I've seen.
Hope it might be useful to someone.

SmartGauge Electronics - Narrowboat AC systems
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Old 29-04-2014, 08:10   #11
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Re: ELCI and Isolation Transformer

Quote:
Originally Posted by gpeacock View Post
Dave, thank you so much for clearing up the neutral pigtail issue. I had a preconceived notion in my head and read your previous post the way I wanted to. The ELCI now trips. Feel free to call me stupid.
Im learning lots here. I still have to get through re reading your other post before I decide to float or not float the AC. Now the easy question. If my inverter charger leaks current to DC or my hot water tank shorts and I move the ELCI ahead of the transformer it wont trip correct?
Thanks again for sticking with me through this
Gary
Correct, if the ELCI is ahead (shore side) of the transformer, it will not trip or see faults on the secondary side of the transformer.

FWIW, I have (3) ELCIs, one on the shore side of the IT, the main breaker in the distribution panel, and on the inverter output. I have no GFCI receptacles.
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Old 29-04-2014, 08:17   #12
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Re: ELCI and Isolation Transformer

Thanks guys.
I guess I need to do some more research to sort out the best options for me. I am amazed at the number of very different approaches.
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Old 29-04-2014, 10:27   #13
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Re: ELCI and Isolation Transformer

Quote:
Originally Posted by gpeacock View Post
Thanks guys.
I guess I need to do some more research to sort out the best options for me. I am amazed at the number of very different approaches.
an ELCI on the secondary, where a AC protective earth wire from the neutral of the secondary to the appliances cases can be useful, for example it will trip on any hot faults to appliance case. ( This being the most common fault). The IT will prevent fault currents returning through earth ( i.e. seawater etc) , so it will no trip typically if you touch the hot, but then again you will not get a shock anyway.

So the ELCI on the secondary has some advantages. I personally would fit one, hear a RCBO is about 30 quid, so not a big issue. Equally Id fit one on the primary to protect the primary as well ( but thats just me).

More ELCIs are always better then less !!


and to deal with this

Quote:
If my inverter charger leaks current to DC or my hot water tank shorts and I move the ELCI ahead of the transformer it wont trip correct?
If all these devices are being fed from the IT ( which they should be) , then a secondary ELCI , can be tripped by using the neutral/Ac protective earth wire. Ie the hot water tank will be connected to that wire, which ultimately connects back to the IT, since the ELCI is not detecting current in the AC protective earth wire, and the water heater shorts to the tank , the secondary side ELCI will trip.

detecting AC leakage in DC systems is a bit beyond the scope here.

dave
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