Reverse Polarity Unit.

[Tigerr]

Forgive me if this is a silly question.

The new-to-us boat has a Mastervolt Inverter system, and located just next to it is a consumer tripswitch unit with two green indicator lights. 

one marked 'Ring Main', and one marked 'reverse polarity'.  Each tripswitch has a green light.

The ring main obviously indicates when the ring main is active and supplying 240V, either from the inverter or shoreline. 

But what is the purpose pf the 'reverse polarity' indicator and switch?  I'd have thought reverse polarity was a wiring fault, not a 'green light' state. Can't remember anything like this unit on the previous boat. 

Appreciate any insight. 

 

[nicknorman]

3 minutes ago, Tigerr said:

Forgive me if this is a silly question.

The new-to-us boat has a Mastervolt Inverter system, and located just next to it is a consumer tripswitch unit with two green indicator lights. 

one marked 'Ring Main', and one marked 'reverse polarity'.  Each tripswitch has a green light.

The ring main obviously indicates when the ring main is active and supplying 240V, either from the inverter or shoreline. 

But what is the purpose pf the 'reverse polarity' indicator and switch?  I'd have thought reverse polarity was a wiring fault, not a 'green light' state. Can't remember anything like this unit on the previous boat. 

Appreciate any insight. 

 

Normally it would relate to shore power only, not when powered from the inverter. It would indicate a swap between live and neutral. As you say, this would be a consequence of a wiring fault either in the shore power lead or the wiring inside the shore bollard. I would presume that in the event of reversed polarity in the incoming shore power, the green light would be replaced by a red light.
 

I’ve never really seem much point in these lights - we don’t have one.

Edited November 14, 2023 by nicknorman

[Tracy D'arth]

Its so you know the shore line supply is reversed, not a fault as such, it will work both ways but better to be right. Perhaps they had too many green LEDs.

[Onewheeler]

59 minutes ago, nicknorman said:

I’ve never really seem much point in these lights - we don’t have one.

If you boat on the mainland you'll find reversed polarity or centre tap are not uncommon.

[nicknorman]

1 hour ago, Onewheeler said:

If you boat on the mainland you'll find reversed polarity or centre tap are not uncommon.

All our boating is on the mainland! Normally we only use shore power in the marina, which as far as I know is wired correctly. Our Travelpower is of course centre tap, but that is not a problem as we have a double pole breaker. In fact if you have double pole breakers, is there actually any issue with having L and N reversed? And following on, if you did have such a light, what would you do if it came on to show LN reversed? Panic?

Edited November 14, 2023 by nicknorman

[PeterF]

Our boat manual tells you to disconnect the shore lead.

What is slightly odd is I specified an isolation transformer for the build and the reverse polarity light has still been fitted to the boat side of the IT, reverse polarity can not occur from shore lead reversal. When I queried the builder, the manual warning was for galvanic isolator fitted boats and he missed revising my manual and they fit the reverse polarity lights regardless to avoid arguments with BSS inspectors who would not accept an IT based system did not need one.

[davidg]

Reverse polarity can be dangerous. A friend who worked for H&S at Lucas told me the tale of an electrician working in one of their labs who went to work on the electrical system, turned off the (single pole) mcb and started touching cables.

It didn't end well.

[nicknorman]

1 minute ago, davidg said:

Reverse polarity can be dangerous. A friend who worked for H&S at Lucas told me the tale of an electrician working in one of their labs who went to work on the electrical system, turned off the (single pole) mcb and started touching cables.

It didn't end well.

Since we have a Travelpower which is centre tapped, we have double pole breakers and it would be sensible for all boats to have them, bearing in mind the trivial extra cost. Maybe most do, I don’t know.

31 minutes ago, PeterF said:

Our boat manual tells you to disconnect the shore lead.

What is slightly odd is I specified an isolation transformer for the build and the reverse polarity light has still been fitted to the boat side of the IT, reverse polarity can not occur from shore lead reversal. When I queried the builder, the manual warning was for galvanic isolator fitted boats and he missed revising my manual and they fit the reverse polarity lights regardless to avoid arguments with BSS inspectors who would not accept an IT based system did not need one.

There is no BSS requirement for a reverse polarity light.

[Alan de Enfield]

7 minutes ago, nicknorman said:

There is no BSS requirement for a reverse polarity light.

 

Do you think that has any influence on a BSS examiners interpretation of the rules?

It seems that many examiners take the published requirements as a "start point' and take the opportunity to add their own 'safety requirements'

[ditchcrawler]

46 minutes ago, PeterF said:

Our boat manual tells you to disconnect the shore lead.

What is slightly odd is I specified an isolation transformer for the build and the reverse polarity light has still been fitted to the boat side of the IT, reverse polarity can not occur from shore lead reversal. When I queried the builder, the manual warning was for galvanic isolator fitted boats and he missed revising my manual and they fit the reverse polarity lights regardless to avoid arguments with BSS inspectors who would not accept an IT based system did not need one.

Its not a BSS item as far as I know, maybe they just didn't know how it worked

[nicknorman]

17 minutes ago, Alan de Enfield said:

 

Do you think that has any influence on a BSS examiners interpretation of the rules?

It seems that many examiners take the published requirements as a "start point' and take the opportunity to add their own 'safety requirements'

Only if you pick a bad examiner!

[magnetman]

I have not come across a BS examiner who was concerned with the AC circuits on the Boats. 

 

I must admit I assumed that they were not part of the examination. Maybe they are and I just got good examiners. 

 

 

 

[nicknorman]

2 minutes ago, magnetman said:

I have not come across a BS examiner who was concerned with the AC circuits on the Boats. 

 

I must admit I assumed that they were not part of the examination. Maybe they are and I just got good examiners. 

 

 

They are mostly just recommendations for a private boat.

[magnetman]

8 minutes ago, nicknorman said:

 

They are mostly just recommendations for a private boat.

 

I often get temporary significant hearing problems when BS Scheme recommendations are discussed.

 

Maybe this is why I seem to have missed AC as a potential issue. 

 

 

 

 

[Alan de Enfield]

2 hours ago, nicknorman said:

Only if you pick a bad examiner!

 

Different people will have a different idea if an examiner is a good one or a bad one.

 

If you want to ensure your boat complies and is 'safe' as the BSS define it, then you want one who is a stickler for the rules and checks everything.

 

If you simply want a piece of paper to enable you to get a licence then you just want one who sits in the saloon, has a mug of tea and a few Jaffa Cakes and writes out the certificate.

 

 

[nicknorman]

9 minutes ago, Alan de Enfield said:

 

Different people will have a different idea if an examiner is a good one or a bad one.

 

If you want to ensure your boat complies and is 'safe' as the BSS define it, then you want one who is a stickler for the rules and checks everything.

 

If you simply want a piece of paper to enable you to get a licence then you just want one who sits in the saloon, has a mug of tea and a few Jaffa Cakes and writes out the certificate.

 

 

I’d be quite happy with an examiner who is a stickler for the rules and checks everything. What I don’t want is an examiner with a bee in his bonnet who invents new rules.

[ditchcrawler]

7 minutes ago, nicknorman said:

I’d be quite happy with an examiner who is a stickler for the rules and checks everything. What I don’t want is an examiner with a bee in his bonnet who invents new rules.

I go along with that.