Reverse polarity

[Andy G]

I'm flat out knowing my AC from my DC, Ohms from volts. So acknowleding this, my question is why does my circuit board on the IG have a Reverse Polarity light and what does it mean in practical terms if it comes on?

 

[FF]

practical terms if it comes on?

ON an AC circuit it can mean your ground wire is lost or reversed and you could get line voltage thru your body with some appliances.

 

[Keith]

On my current boat, an insurance survey had me add one. On my past boat, it went off once when I plugged into a homeowners shore power outlet. I just disconnected and ran the genset when needed.

 

[Larry M]

This came from another forum:*
The most important issue is whether the power supply polarity is correct.* If reversed, the Neutral and Hot legs are switched. Then all your breakers interrupt the Neutral, not the Hot, so your whole system is energized even when the breaker is off. The breaker will turn of the equipment, but it is still energized. A fault can then start a fire, since the breaker won't sense the ground fault, and current will flow until something melts and the circuit is broken. There's also the danger of electrical shock, for the same reason.

 

[Sisuitl]

Always, always check this light after connecting to shore power but immediately before or immediately after flipping the transfer switch from "genset" to "shore", depending how your boat is wired. Do not ignore the fault light. Disconnect immediately and find out what the problem is.

How do I know this? Let's just say, good judgement comes from experience and experience is the result of bad judgement. We were having intermittent problems with the fault light coming on occasionally at one particular dock. I ignored it and the the problem turned out to be a faulty neutral connection in the male plug of our shore cord. I guess something about the way the cord hung from that particular box caused the problem to show up.

We got lucky. Toasted male plug that needed to be replaced, blown breakers, and no damage from the freezing temperatures of that two week period the boat sat at the dock. And no deaths.

At least, none that could be traced to us.

 

[Phil Fill]

We were required by the insurance company to bring the Eagle up to ABYC standard which requires a DOUBLE throw breaker with polarity light installed between the boat shore plug out let and the main power panel AC selector switch.* Many electrical fire are between the shore power plug/cord and the AC breaker which*on many boats is after*the AC selector switch.** A*DOUBLE throw breaker is required so if the polarity is reversed*it will still break*

 

[Andy G]

Ok thanks for that everyone. So the Reverse polarity light is a warning indicator that all is not well.

FF" ON an AC circuit it can mean your ground wire is lost or reversed and you could get line voltage thru your body with some appliances."

Does this mean that the ELCB (Earth trip switch) will fail to trip?

 

[FF]

I am not aware of the ground wire being disconnected by any type of breaker.

The usual 2 breaker wires cut are the hot and neutral in most panels ..

 

[ARoss]

I think I posted this once, a while ago, but maybe worth repeating.* I have one of these gizmos plugged into an* AC outlet to check every time I hook up shore power

 

[FF]

Does this mean that the ELCB (Earth trip switch) will fail to trip?


Are you referring to a GFI "Ground Fault Interupter?

 

[Sisuitl]

ARoss wrote:
I think I posted this once, a while ago, but maybe worth repeating.* I have one of these gizmos plugged into an* AC outlet to check every time I hook up shore power

*So, let me get this straight. On the one hand, we have a $100 added-feature light soldered into an expensive marine power panel that usually only indicates one failure mode. On the other hand, we have an $8 gadget carried by every residential electrician in North America that actually gives better information on more failure modes than the panel light does.

I dunno, seems lacking a certain je ne sais quois. I might have to set fire to a few $20s when I pick one up tomorrow just to make things feel right.

 

[RickB]

Sisuitl wrote:*On the other hand, we have an $8 gadget carried by every residential electrician in North America that actually gives better information on more failure modes than the panel light does.

*That isn't quite a fair evaluation. The built in reverse polarity warning tells you if the shore power is improperly connected. The little outlet tester tells you if the outlet you are about to use is connected properly.

The reason every residential electrician in North America carries one is because there is no way to look at an outlet and tell if it is wired properly. The same applies to a boat.

 

[FF]

On the one hand, we have a $100 added-feature light soldered into an expensive marine power panel that usually only indicates one failure mode. On the other hand, we have an $8 gadget carried by every residential electrician in North America that actually gives better information on more failure modes than the panel light does.

Yup,

Making 50 million of something in China is always cheaper than hand assembling one of anything anywhere.

 

[rwidman]

FF wrote:
On the one hand, we have a $100 added-feature light soldered into an expensive marine power panel that usually only indicates one failure mode. On the other hand, we have an $8 gadget carried by every residential electrician in North America that actually gives better information on more failure modes than the panel light does.

Yup,

Making 50 million of something in China is always cheaper than hand assembling one of anything anywhere.

*

It's not a "$100.00 added in feature", it's part of any modern marine electrical panel.* It is not possible to put a specific cost on this feature.

As far as it's purpose, it's been said several different ways, but the bottom line is, there is a problem with the power source (dock power or portable generator) that needs to be corrected immediately.* Disconnect the boat from the source untill the problem is corrected.

*

 

[Andy G]

I am resurrecting this very old thread as I have a specific question that I hope some of the more electrically minded memebers may be able to answer. The problem is my reverse polarity(RP) light on the 240volt section of my main board has come on.


"The built in reverse polarity warning tells you if the shore power is improperly connected." This was from RickB 2011, he certinally knows what he is talking about.

My question. If the RP light comes on,can I assume the problem lays with the connection/lead from the boat to the shore power pedestal Or could the problem lie elsewhere? (The 240volt supply from the generator is fine, though the RP light stays on).

 

[Insequent]

The RP light should never be on. If it is you have a problem that needs to be fixed. Best get a marine sparky on the case.

Your original question was back in 2011. Have you had RP coming on for over 14 years?

 

[Andy G]

No, it's new issue. We had a new shore power lead made up a couple of weeks ago, so that is a possibility. However the power lead had been in operation for a couple of weeks before the reverse polarity light came on.

I guess it's time to have a chat with the electricians at the marina.

 

[Insequent]

A power lead would be the most common source of RP faults. But in your case, particularly with generator causing it as well, there is something amiss with the boats wiring. As noted upthread under some circumstances it can be hazardous, as in lethal. Curious as to cause, would appreciate you keeping us updated on the outcome.

 

[twistedtree]

I agree with the above. You (or someone) need to check step by step to check polarity. The galvanic isolator things that the line and neutral wires are reversed. You will need to figure out if there actually is a reversal, and where. Or it may be a bad galvanic isolator. If the problem occurred the first time you used the new lead it would suggest the lead was mis-wired. Have you been plugged into the same shore power outlet, and now you are getting an error? If that's the case then it would seem most likely to be a failed galvanic isolator or perhaps the marina made some change on their side.

 

[SteveK]

I thought reverse polarity light is between neutral and ground. When a neutral becomes a hot the RP lights up. This occurs when a cable hot and neutral are wired in reverse.

 

[Fleming]

I thought reverse polarity light is between neutral and ground. When a neutral becomes a hot the RP lights up. This occurs when a cable hot and neutral are wired in reverse.

Close. Any voltage difference between the neutral and the grounding conductor will cause the RP to light. There are a few different causes of it along with an actual reverse polarity.

 

[Andy G]

I agree with the above. You (or someone) need to check step by step to check polarity. The galvanic isolator things that the line and neutral wires are reversed. You will need to figure out if there actually is a reversal, and where. Or it may be a bad galvanic isolator. If the problem occurred the first time you used the new lead it would suggest the lead was mis-wired. Have you been plugged into the same shore power outlet, and now you are getting an error? If that's the case then it would seem most likely to be a failed galvanic isolator or perhaps the marina made some change on their side.

I looked into that. I tried changing the marina pedestal supply with my next door neighbour who was not experiencing any issues. No luck, still showing Reverse polarity.

I have asked the electrician to look into it, waiting on a reply.

 

[jgwinks]

If the new cable has ends that you can take apart it's an easy check. The terminals inside the plugs should be color coded, on both ends the black wire goes to the black or brass colored screw, white wire goes to white or silver colored. Green wire goes to the green screw. If whoever made the cable got it wrong, a stern talking to is in order.

 

[Insequent]

If the new cable has ends that you can take apart it's an easy check. The terminals inside the plugs should be color coded, on both ends the black wire goes to the black or brass colored screw, white wire goes to white or silver colored. Green wire goes to the green screw. If whoever made the cable got it wrong, a stern talking to is in order.

That doesn't very much. Here in Australia we use Euro colour coding.....

Brian

 

[jgwinks]

That doesn't very much. Here in Australia we use Euro colour coding.....

Brian

Ok, but you can still check that the same color is connected to the same terminal on each end. It really doesn't matter in a practical sense what color goes to which as long as it's the same on both ends.

 

[twistedtree]

Or use a meter to check without taking things apart. But since things worked OK for a while with the new power lead, it's wired correctly. Since the problem started without other surrounding changes, it would seem that something has broken. Maybe the galvanic isolator, or perhaps a ground has failed.

 

[SteveK]

Or use a meter to check without taking things apart. But since things worked OK for a while with the new power lead, it's wired correctly. Since the problem started without other surrounding changes, it would seem that something has broken. Maybe the galvanic isolator, or perhaps a ground has failed.

Please explain how the galvanic isolator contributes to reverse polarity. Here is a diagram of the reverse polarity light wiring. The GI would be inline of the ground wire.

 

[SteveK]

HERE is an explanation from Blue Seas

 

[RickyD]

I hope this isn't off topic but my boat has the incoming receptical on the strb side and I like my end tie docked on the port. I had to add 20ft to my 50amp dock cable. I occasionally would lose one leg of my incoming power which would have me running ac through the inverter. Not good. Taking the connector apart there were burn marks. I tried to find another system for connection but they weren't made so I took the connector apart and wired it together wrapped heavily in electrical tape. Not good looking but it has been perfectly effective.

 

[twistedtree]

Please explain how the galvanic isolator contributes to reverse polarity. Here is a diagram of the reverse polarity light wiring. The GI would be inline of the ground wire.
View attachment 171617

It wouldn't reverse the polarity. But I'm thinking it might be falsely indicating a reversal.