15kva isolation transformer help

Thread Starter

duncan mccallie

Joined Apr 2, 2015
27
Hi,
I’m new to this forum, and uncertain where to post this....I’m hoping someone will be kind enough to walk me through wiring an isolation transformer I’m replacing on a boat. The previous unit was a Charles Industries 12.5 KVA . Single phase 240 volt primary and 240 secondary. The neutral didn’t come aboard.
The replacement unit is a GE 15 KVA. I will post a photo of the ID/wiring info. It’s unclear to me how to hook this one up. Where do I get the neutral on the secondary side? And do I still leave the neutral ashore on the primary side?
Please be kind, I’m old and sensitive :)

Thanks,
SparkyF6EEB621-607D-4D4F-83E6-A1B38A6E537D.jpeg
 

MaxHeadRoom

Joined Jul 18, 2013
19,466
The neutral is arbitrary, IOW it is no different from the 'live' conductor, it is just one that is chosen to be earth grounded.
So if you want/need to set up a neutral, one side of the secondary has to be connected to a valid earth or ground source.
If the primary is fed from a 120v shore service, then there should be a service earth conductor there to reference to.
This secondary terminal then provides a source of both neutral and GND conductors.
See attached, transformer 1T terminal X2
BTW, if you just want complete isolation, then don't set up the neutral (GND).
Max.
 

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Reloadron

Joined Jan 15, 2015
4,749
Was this pretty much your original transformer and setup?

May I assume your original shore power primary was setup for 240 volts and not 480 volts?

If original shore power setup was 240 volts and you want 240 volts split phase secondary 120V _ 0V_ 120V your new transformer will do that. On the new transformer connect H1 and H3 together, connect H2 and H4 Together so you have H1&H3 and H2&H4 forming two lines for your 240 Volt shore power. Shore power ground can connect to the transformer can using a grounding stake. The isolated secondary would be X2 and X3 tied together and they become your 120 volt Neutral. X1 to X2&X3 are 120 volts, X4 to X2&X3 is 120 volts and X1 to X4 is your 240 Volts. Pretty much as in the manual I linked to which should be very close to what you originally had.

Ron
 

MisterBill2

Joined Jan 23, 2018
4,594
The main purpose of an isolation transformer is to provide isolation. The shore 240 volt power goes to the primary side, connected for 240 volts exactly as described ( H1, H2, H3, H4). The 240 volt boat wiring connects to the secondary, connected for 240 volts, exactly as shown. But if the secondary was actually used to provide both 120 and 240 volts, that is a bit different yet. And the neutral from the shore power stays on shore.
 

MisterBill2

Joined Jan 23, 2018
4,594
@duncan mccallie keep in mind that if you use an isolated supply, i.e. no neutral, then both legs should be fused.
Using a neutral is optional.
Max.
Max, I am presuming that since the TS claims to be replacing a transformer, that the previous installation was OK. Of course entrance circuit protection must be provided, in a large boat that may visit strange ports I prefer breakers that can be reset, since fuses may be a challenge to find in some areas.
 

MaxHeadRoom

Joined Jul 18, 2013
19,466
I prefer breakers that can be reset, since fuses may be a challenge to find in some areas.
Fuses, breakers, either way, Both lines should have one or the other in place, rather that the L & N single device in the 'hot' lead only for e.g. if one secondary conductor not set up for a neutral.
Max.
 
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MisterBill2

Joined Jan 23, 2018
4,594
Fuses, breakers, either way, Both lines should have one or the other in place, rather that the L & N single device in the 'hot' lead only for e.g. if one secondary conductor not set up for a neutral.
Max.
We were not given any clue about the load side of the transformer's connections, other than "240 volts".
BUT since it is called an isolation transformer there needs to be some isolation, meaning not grounding any portion of the secondary circuit.
 

Reloadron

Joined Jan 15, 2015
4,749
The thread starter did mention what he was replacing. While I could not find a 12.5 KVA flavor I did see a 12.0 KVA Flavor.

While there are a few configurations Figures 1 and 2 pretty well show how a Marine Isolation Connections are made. The 240 volt reflects a split phase where on shipboard side Neutral and Ground are tied. Since the GE replacement is a 15 KVA weighing in at 267 Lbs we can pretty much figure a large boat. Until the thread starter provides more information this is as good as it gets? :)

Ron
 

MisterBill2

Joined Jan 23, 2018
4,594
The thread starter did mention what he was replacing. While I could not find a 12.5 KVA flavor I did see a 12.0 KVA Flavor.

While there are a few configurations Figures 1 and 2 pretty well show how a Marine Isolation Connections are made. The 240 volt reflects a split phase where on shipboard side Neutral and Ground are tied. Since the GE replacement is a 15 KVA weighing in at 267 Lbs we can pretty much figure a large boat. Until the thread starter provides more information this is as good as it gets? :)

Ron
Exactly! My problem is a lack of mind reading ability, even in person or on the phone. And at any distance I am unable to even get a hint. Evidently a large number of participants seem to believe otherwise.
 

MaxHeadRoom

Joined Jul 18, 2013
19,466
May I assume your original shore power primary was setup for 240 volts and not 480 volts?

If original shore power setup was 240 volts and you want 240 volts split phase secondary 120V _ 0V_ 120V your new transformer will do that.
Ron
Ron, although if connecting that way, the VA will be reduced (halved) as the optional connections are series secondary for 240, parallel for 120v, splitting them halves the current capability on each of the 120v.
Each 120v winding capacity. This would affect a maximum 120v individual load level possible..
Max.
 

Reloadron

Joined Jan 15, 2015
4,749
Guys, I believe what this comes down to is absolutely yes, more information is needed. Especially since we never saw the original or last configuration.

Unrelated note but sometimes when things go wrong on a boat with power they can really go very wrong. I remember this mishap very well. Like most news stories never did read later what the actual cause was?

Ron
 

Thread Starter

duncan mccallie

Joined Apr 2, 2015
27
Guys, I believe what this comes down to is absolutely yes, more information is needed. Especially since we never saw the original or last configuration.

Unrelated note but sometimes when things go wrong on a boat with power they can really go very wrong. I remember this mishap very well. Like most news stories never did read later what the actual cause was?

Ron
Thank you everybody here for your help. We got a little snow here in the northwest and the ensuing panic. Sorry to be slow in responding.
The boat is 67 feet. The transformer I’m replacing is the exact model ‘ reloadron’ posted initially. The shore power is 240 and there is a 50amp breaker on the dock.
The secondary is split and 120 and 240 are used aboard. Please let me know if there is any additional information necessary.
 

Thread Starter

duncan mccallie

Joined Apr 2, 2015
27
Thank you everybody here for your help. We got a little snow here in the northwest and the ensuing panic. Sorry to be slow in responding.
The boat is 67 feet. The transformer I’m replacing is the exact model ‘ reloadron’ posted initially. The shore power is 240 and there is a 50amp breaker on the dock.
The secondary is split and 120 and 240 are used aboard. Please let me know if there is any additional information necessary.
Sobering story about the electrocution. Exactly the issue I’m hoping to avoid. That and stray current corrosion from surrounding vessels in the moorage.
 

MaxHeadRoom

Joined Jul 18, 2013
19,466
I know nothing of any regulations concerning powering a water vessel from shore power, may be a check to see what, if any regs there actually are.;)
Personally I would have thought that a boat fed from shore power would have a grounded neutral?
@duncan mccallie do you need 240v?
Max.
 

Thread Starter

duncan mccallie

Joined Apr 2, 2015
27
I know nothing of any regulations concerning powering a water vessel from shore power, may be a check to see what, if any regs there actually are.;)
Personally I would have thought that a boat fed from shore power would have a grounded neutral?
@duncan mccallie do you need 240v?
Max.
Thanks Max, Yes I use 240VAC for Heat, Clothes Dryer, Watermaker, etc. Most of the rest is 120.
 

MaxHeadRoom

Joined Jul 18, 2013
19,466
If you set up the transformer in 120-0-120 as Ron suggests, it will pay to attempt to balance all 120v outlets between the anticipated 120v loads.
This will ensure that when several high 120v loads are present, the neutral current will be much lower than the total 120v load currents.
Connect as per 240v and the X2-X3 wil be the neutral.
Max.
 

Reloadron

Joined Jan 15, 2015
4,749
OK, thought it may be configured like that. Working from my link and assuming 240 volt shore power H1 and H3 get tied and H2 and H4 get tied on the new transformer, that sets up a 240 volt primary side and I would take your shore power ground and neutral and using a lug tie them to the new transformer can and that assumes the can is not on a steel bulkhead or mounted to metal (boat's ground). On the secondary X2 and X3 are tied and become Neutral and Ground as shown in the original transformer manual. Then try and split / balance the loads as Max suggested. That's about it. Your mains shore and ship power will be isolated. Yeah, a 63 footer is a nice size boat. My largest was a 30 foot 1963 Chris Craft Cavalier Express a long, long time ago on the east coast. Everything was 12 VDC. :)

Ron
 

Thread Starter

duncan mccallie

Joined Apr 2, 2015
27
OK, thought it may be configured like that. Working from my link and assuming 240 volt shore power H1 and H3 get tied and H2 and H4 get tied on the new transformer, that sets up a 240 volt primary side and I would take your shore power ground and neutral and using a lug tie them to the new transformer can and that assumes the can is not on a steel bulkhead or mounted to metal (boat's ground). On the secondary X2 and X3 are tied and become Neutral and Ground as shown in the original transformer manual. Then try and split / balance the loads as Max suggested. That's about it. Your mains shore and ship power will be isolated. Yeah, a 63 footer is a nice size boat. My largest was a 30 foot 1963 Chris Craft Cavalier Express a long, long time ago on the east coast. Everything was 12 VDC. :)

Ron
Thanks Ron,
That should do it. I’ll watch for smoke :)
I built this thing over more years than I want to admit.
 

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MisterBill2

Joined Jan 23, 2018
4,594
On a boat, or any place else, for that matter, as soon as one side of the line is tied to "ground", every point on the other side becomes a shock hazard relative to everything that might be connected to ground. ^This includes feet on a wet floor and any faucet, and most metal appliances. In our homes we have no choice because the distribution system has one side grounded for a number of reasons. But once we have an actual ISOLATION transformer we no longer have that hazard, the shock can only be between the two sides, and all of the grounded items are open circuit to the shock source. The hazardous voltage between the two sides of the line is still there, but it is less likely to get between those two than between one of them and ground.
Thus it is time to stop and think carefully before connecting all of the conductive structure of a boat to one side.

AND NOW, I am wondering why the previous transformer had to be replaced. A 15 KVA transformer of any quality is a fairly expensive item, and so there must be a real reason for replacing it. Hopefully whatever brought about the need for the replacement has been adequately addressed.
 
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