Cruisers Forum
 


Join CruisersForum Today

Reply
  This discussion is proudly sponsored by:
Please support our sponsors and let them know you heard about their products on Cruisers Forums. Advertise Here
 
Thread Tools Search this Thread Rate Thread Display Modes
Old 19-10-2019, 04:40   #1
Moderator
 
Dockhead's Avatar

Cruisers Forum Supporter

Join Date: Mar 2009
Location: Cowes (Winter), Helsinki (Summer); Cruising the Baltic Sea this year!
Boat: Cutter-Rigged Moody 54
Posts: 25,644
Shore Power Connections -- Again

People, check your shore power connections regularly for burned contacts. Any plug like this which handles significant volumes of power is subject to this, and can cause a fire.


I got rid of the odious Marinco twist plug my boat came with, some years ago. I temporarily replaced it with a European blue plug, which is a far superior design. I bought a SmartPlug but didn't get around to installing it until just yesterday.


AND I discovered that the blue plug, too, had been burning its little contacts, although I had not detected the temperature in my regular infrared thermometer checks.


This is really dangerous I knew someone who lost a boat because of a fire which apparently started at the shore power inlet. Once fiberglass starts to burn, it's pretty hard to put out.


I hope the SmartPlug is the final solution for this, but we shall see. I am impressed with the construction of it, especially the heavy duty wire connectors, and the elaborate water seals. I am using a 32 amp one for shore power connections which do not exceed 16 amps, so it should be overbuilt for the job -- we shall see.




I worry about the sockets down below, as well. My boat has the UK ones, taking plugs like this:


Click image for larger version

Name:	ukplugexternal-content.duckduckgo.com.jpg
Views:	148
Size:	23.8 KB
ID:	201754


rated at 13 amps each. These are good plugs, with robust contacts and lots of contact area, and built-in fuses in each one, but I sometimes get some heating of them when I'm using them with electrical heaters or other large consumers. It would sure be nice to have thermal protection in the socket or plug, but I've never seen such a socket or plug.
__________________

__________________
"Parce que je suis heureux en mer, et peut-Ítre pour sauver mon ame. . . "
Dockhead is offline   Reply With Quote
Old 19-10-2019, 05:39   #2
Beloved by chandlers everywhere

Cruisers Forum Supporter

Join Date: Feb 2017
Location: Med
Boat: Dufour 455 GL
Posts: 210
Re: Shore Power Connections -- Again

My boat has the shore power cable hard-wired into an onboard fuse. I was going to install a Mastervolt 316 socket somewhere around the transom, but after reading your post I might think it over again. The disadvantage of the hard-wired cable is that even though the cockpit locker (where the cable lives) has a conduit of sorts to allow the lid to close over the deployed cable, the fiberglass edges of the locker lid inevitably end up chewing up the cable a little every time.

Considering some of the practices I observe on charter boats around me, the fire is almost guaranteed to start on the next boat over
__________________

LongRange is online now   Reply With Quote
Old 19-10-2019, 05:50   #3
Moderator
 
Dockhead's Avatar

Cruisers Forum Supporter

Join Date: Mar 2009
Location: Cowes (Winter), Helsinki (Summer); Cruising the Baltic Sea this year!
Boat: Cutter-Rigged Moody 54
Posts: 25,644
Re: Shore Power Connections -- Again

Quote:
Originally Posted by LongRange View Post
My boat has the shore power cable hard-wired into an onboard fuse. I was going to install a Mastervolt 316 socket somewhere around the transom, but after reading your post I might think it over again. The disadvantage of the hard-wired cable is that even though the cockpit locker (where the cable lives) has a conduit of sorts to allow the lid to close over the deployed cable, the fiberglass edges of the locker lid inevitably end up chewing up the cable a little every time.

Considering some of the practices I observe on charter boats around me, the fire is almost guaranteed to start on the next boat over

I know a few people who use hard wired shore power cables. It's a great solution but for the issue you mention. I would not, personally, accept the cable's getting damaged in the locker lid -- that can cause a fire, too.
__________________
"Parce que je suis heureux en mer, et peut-Ítre pour sauver mon ame. . . "
Dockhead is offline   Reply With Quote
Old 19-10-2019, 07:00   #4
Registered User
 
Auspicious's Avatar

Join Date: Jun 2003
Location: Chesapeake Bay
Boat: HR 40
Posts: 2,474
Send a message via Skype™ to Auspicious
Re: Shore Power Connections -- Again

Quote:
Originally Posted by Dockhead View Post
I know a few people who use hard wired shore power cables. It's a great solution but for the issue you mention. I would not, personally, accept the cable's getting damaged in the locker lid -- that can cause a fire, too.
Me.

Agree on not damaging the cable in the routing. I use the gutted old Marinco inlet to feed the cable through.

Note to others: have extra nuts and washers for the connection. *grin*
__________________
S/V Auspicious
AuspiciousWorks
Beware cut and paste sailors
Auspicious is offline   Reply With Quote
Old 19-10-2019, 07:08   #5
Registered User

Join Date: Jun 2019
Location: Rochester, NY
Boat: Chris Craft Catalina 381
Posts: 43
Re: Shore Power Connections -- Again

For the interior plugs, most connectors like that will get slightly warm when operating close to rated current. That's expected and not a problem. It's any arcing or if they get excessively hot that's a problem and risks the contact getting worse, causing more heat, etc. until it melts down.

For shore power plugs, using connectors rated for more than you'll pull through them is a good idea. In addition, follow the 80% rule that's common for land based electrical in the US. Maximum continuous draw is 80% of the circuit rating. So for a 30A shore inlet, that's 24A max continuous, anything above can only be a short spike. For a 50A inlet, the limit is 40A.

For the US based people, I personally advise switching to 50A shore power inlets and cords even if you don't need the extra amps. Yes, the cords are bigger and heavier to deal with. But the plugs are much more robust (which matters at the dock end where you can't control the plug), so you get much more solid connections at most marinas and can put an adapter on to plug into a 30A shore plug for the times where 50A isn't available.

Another shore power safety note. If you have 30A cords and boat plugs, don't use those 50A to dual 30A adapters. If you want or need to use one, build your own so you can install a breaker in it to protect the 30A outlet legs. The off the shelf ones aren't current limited, so you're left with a 50A dock breaker protecting cable that's only good for 30A (between the dock breaker and the boat breaker). In other words, if something shorts before the boat breaker, the inlet, inlet wiring and shore cable will go up in smoke.
rslifkin is offline   Reply With Quote
Old 19-10-2019, 07:55   #6
Registered User

Join Date: Jan 2014
Location: Panama City FL
Boat: Island Packet 32 Keel/CB
Posts: 443
Re: Shore Power Connections -- Again

Quote:
Originally Posted by rslifkin View Post
If you have 30A cords and boat plugs, don't use those 50A to dual 30A adapters. If you want or need to use one, build your own so you can install a breaker in it to protect the 30A outlet legs. The off the shelf ones aren't current limited, so you're left with a 50A dock breaker protecting cable that's only good for 30A (between the dock breaker and the boat breaker). In other words, if something shorts before the boat breaker, the inlet, inlet wiring and shore cable will go up in smoke.

Don't have issue with most of your observations but the above is off base a little. Assuming that the SP and yacht end's of the electrical are all up to snuff, then the two 30 Amp yacht mains will take care of overloads. If a short circuit or ground fault happens between the 50 Amp supply and the yacht, the 50 amp breaker will clear the problem as quickly as the 30 amp.

In electrical systems overloads and short circuit/ ground faults are significantly different problems. Just happens that modern circuit breaker will clear both conditions so they often get conflated.


Frankly
Frankly is offline   Reply With Quote
Old 19-10-2019, 08:04   #7
Registered User
 
S/V Illusion's Avatar

Join Date: Oct 2007
Location: Lakewood Ranch, FLORIDA
Boat: Alden 50, Sarasota, Florida
Posts: 2,227
Re: Shore Power Connections -- Again

There problems can be easily prevented simply by using any of the myriad copper coating greases on the market. A little bit periodically on the connections serves to enhance conductivity and preclude moisture-corrosion of the contacts.

It also serves to ensure good electrical conductivity and prevent moisture on all electrical and coax connections.
S/V Illusion is offline   Reply With Quote
Old 19-10-2019, 08:12   #8
Registered User

Join Date: Oct 2015
Posts: 1,545
Re: Shore Power Connections -- Again

Routing a hardwired shore power cord out from a locker is a problem that is so very easily solved it should not deter you from considering this modification. There really is no need for a cord that plugs into the outside of the boat. These connections cause so many problems for so many people I am surprised it is still a standard for almost all yacht builders.

On our boat the manufacturer solved this problem but simply putting a notch in the edge of the locker and the splash wall and having a short piece of soft rubber rod on a cord to seal the gap when sailing. It has worked a champ for 25 years and twice around the world. I would never go back to a boat side plug for shore power inlet.

The comment about not operating any part of the electrical system at 100% of load continuously is also a very good one. We have a Victron Multi inverter/charger with it's peaking ability that allows us to run two 8000BTU AC units and a water heater, plus misc household appliances all on a 30AMP shore power circuit that we limit to no more than a 25 Amp peak draw. Not only do we never stress the shore power system, we also never trip the shore power breaker at 2AM on a rainy cold night...
billknny is offline   Reply With Quote
Old 19-10-2019, 08:39   #9
Moderator
 
Dockhead's Avatar

Cruisers Forum Supporter

Join Date: Mar 2009
Location: Cowes (Winter), Helsinki (Summer); Cruising the Baltic Sea this year!
Boat: Cutter-Rigged Moody 54
Posts: 25,644
Re: Shore Power Connections -- Again

Quote:
Originally Posted by billknny View Post
Routing a hardwired shore power cord out from a locker is a problem that is so very easily solved it should not deter you from considering this modification. There really is no need for a cord that plugs into the outside of the boat. These connections cause so many problems for so many people I am surprised it is still a standard for almost all yacht builders.

On our boat the manufacturer solved this problem but simply putting a notch in the edge of the locker and the splash wall and having a short piece of soft rubber rod on a cord to seal the gap when sailing. It has worked a champ for 25 years and twice around the world. I would never go back to a boat side plug for shore power inlet....



Thanks. That's pretty convincing. If I ever have the good fortune to do a new build, I'll take this to heart. For this to work really well, you would need a special locker for the shore power cord which protects the cord and connection from the weather when not in use, and provides a fair lead to the cord when you're using it. Should not be all that hard to implement.
__________________
"Parce que je suis heureux en mer, et peut-Ítre pour sauver mon ame. . . "
Dockhead is offline   Reply With Quote
Old 19-10-2019, 08:41   #10
Moderator
 
Dockhead's Avatar

Cruisers Forum Supporter

Join Date: Mar 2009
Location: Cowes (Winter), Helsinki (Summer); Cruising the Baltic Sea this year!
Boat: Cutter-Rigged Moody 54
Posts: 25,644
Re: Shore Power Connections -- Again

Quote:
Originally Posted by rslifkin View Post
. . . For shore power plugs, using connectors rated for more than you'll pull through them is a good idea. In addition, follow the 80% rule that's common for land based electrical in the US. Maximum continuous draw is 80% of the circuit rating. So for a 30A shore inlet, that's 24A max continuous, anything above can only be a short spike. For a 50A inlet, the limit is 40A. ..

The "80% Rule"? I never heard of such a thing. I always assumed that the ratings were for continuous use, and were calculated conservatively. If what you say is true, it's a totally different situation. And would explain a lot of my experiences, so you may have made a significant contribution to my education


Now I'm going to have to read up on this. Learn something new every day.




Right off the bat: https://www.electriciansforums.net/t...80-rule.35406/
__________________
"Parce que je suis heureux en mer, et peut-Ítre pour sauver mon ame. . . "
Dockhead is offline   Reply With Quote
Old 19-10-2019, 10:21   #11
Registered User

Join Date: Apr 2018
Location: Scotland
Boat: 42ft Moody Ketch
Posts: 346
Re: Shore Power Connections -- Again

An RCD unit takes care of overloads on your 3 pin UK plug what do they use in houses
The RCD unit at the shore power at the marina will also trip if current to high

If using any 240 v without RCD.s then your daft

Forgot to mention the UK plug you show also has a fuse in it . so that is 3 protections you have on an appliance ,
Marina RCD
Boat RCD
Plug fuse

if you go on fire after that get yourself some lucky white heather
tarian is offline   Reply With Quote
Old 19-10-2019, 10:26   #12
Moderator
 
Dockhead's Avatar

Cruisers Forum Supporter

Join Date: Mar 2009
Location: Cowes (Winter), Helsinki (Summer); Cruising the Baltic Sea this year!
Boat: Cutter-Rigged Moody 54
Posts: 25,644
Re: Shore Power Connections -- Again

Quote:
Originally Posted by tarian View Post
An RCD unit takes care of overloads on your 3 pin UK plug what do they use is houses
The RCD unit at the shore power at the marina will also trip if current to high

If using any 240 v without RCD.s then your daft

I have an RCD of course as my boat was built in the UK in 2001 and it was required. It is rated at 32 amps which is the design capacity of my shore power system.



However, I don't think the RCD, or any breaker, addresses this problem at all. The problem is not overloading the circuit, it's thermal runaway of bad contacts. This can take place at much less than the full rated capacity of the RCD or breaker.
__________________
"Parce que je suis heureux en mer, et peut-Ítre pour sauver mon ame. . . "
Dockhead is offline   Reply With Quote
Old 19-10-2019, 10:41   #13
Registered User

Join Date: Apr 2018
Location: Scotland
Boat: 42ft Moody Ketch
Posts: 346
Re: Shore Power Connections -- Again

Quote:
Originally Posted by Dockhead View Post
I have an RCD of course as my boat was built in the UK in 2001 and it was required. It is rated at 32 amps which is the design capacity of my shore power system.



However, I don't think the RCD, or any breaker, addresses this problem at all. The problem is not overloading the circuit, it's thermal runaway of bad contacts. This can take place at much less than the full rated capacity of the RCD or breaker.
You need an RCD with many different ratings and have separate roles for each trip unit which will allow you to rate you loads to the trip Fuse . i,e your water heater would be on a separate trip. your ring circuit on another your battery charger on another , this allows for selective loading and your RCD to work for you .
the Marina trip fuse is rated to protect your cable to boat you RCD unit to protect all cables leaving the RCD to their Units and then everything plugged in with a UK plug has a fuse .
To test your RCD grind through a 240v cable and see what happens , Nothing as the RCD will trip saving your life , because you have rated it correctly.

Thermal runaway is also protected via the above , To prevent thermal runaway, well-designed electronic systems typically incorporate current limiting protection, such as thermal fuses, circuit breakers, or PTC current limiters
tarian is offline   Reply With Quote
Old 19-10-2019, 10:59   #14
Moderator
 
Dockhead's Avatar

Cruisers Forum Supporter

Join Date: Mar 2009
Location: Cowes (Winter), Helsinki (Summer); Cruising the Baltic Sea this year!
Boat: Cutter-Rigged Moody 54
Posts: 25,644
Re: Shore Power Connections -- Again

Quote:
Originally Posted by tarian View Post
You need an RCD with many different ratings and have separate roles for each trip unit which will allow you to rate you loads to the trip Fuse . i,e your water heater would be on a separate trip. your ring circuit on another your battery charger on another , this allows for selective loading and your RCD to work for you .
the Marina trip fuse is rated to protect your cable to boat you RCD unit to protect all cables leaving the RCD to their Units and then everything plugged in with a UK plug has a fuse .
To test your RCD grind through a 240v cable and see what happens , Nothing as the RCD will trip saving your life , because you have rated it correctly.

Thermal runaway is also protected via the above , To prevent thermal runaway, well-designed electronic systems typically incorporate current limiting protection, such as thermal fuses, circuit breakers, or PTC current limiters

With respect, I think there is a lot of confusion in this, potentially dangerous confusion.


A burned contact or otherwise high resistance contact can start a fire with the circuit operating at considerably less than its rated capacity, and without any residual current fault. So neither RCD nor breaker will prevent every fire started this way. A thermal fuse would do it, but this is an entirely different device which only works if it is mounted exactly in the device which is overheating. I've never seen a thermal fuse in any shore power connector or indeed in any British standard mains socket or plug, although it would be a good thing to have. I believe the early SmartPlugs had something like this but were removed for some reason; in any case my SmartPlug does not have a thermal fuse.


I believe you are also confused about the difference between RCD's and circuit breakers. An RCD is not a current limiting device -- it is designed to interrupt a circuit when a ground fault is detected (a measured difference, even tiny, between the current flowing between the neutral and that flowing through line; see: https://en.wikipedia.org/wiki/Residual-current_device). This function would be useless to prevent a fire caused by an overheated shore power connector. My boat's RCD is combined with a 32 amp circuit breaker which does limit current taken by the shore power system to 32 amps, but a fire can happen in a high resistance connection at far less than 32 amps, so this is also fairly useless in preventing that.


Branch circuits on my boat are protected by a bank of 12 circuit breakers with capacity ranging from 6 amps to 16 amps. These, again, would do nothing to stop a fire caused by high resistance in a plug/socket connection. And they are not RCD's; they are ordinary circuit breakers.
__________________
"Parce que je suis heureux en mer, et peut-Ítre pour sauver mon ame. . . "
Dockhead is offline   Reply With Quote
Old 19-10-2019, 11:32   #15
CF Adviser
 
Pelagic's Avatar

Cruisers Forum Supporter

Join Date: Oct 2007
Boat: Van Helleman Schooner 65ft StarGazer
Posts: 8,595
Re: Shore Power Connections -- Again

Totally agree, inboard plugs for shore power cables are a "failure waiting to happen".

Taking a page from Super yachts, my 60a shore power cable is hardwired within a Junction Box inside the engineroom and the cable stored below the Isolation Transformer

When needed. Cable without a shore plug is fed thru a small.engine room cowled vent .....out a scupper and on to dock.

With an assortment of shore plugs, it takes me about 5 minutes to make the shore side connection.

Luckily, having a generator and ample solar takes the urgency out of connecting to shore power.

IF I was doing frequent day sails from a dock, I would simply disconnect cable lugs from engine room box and leave cable ashore.
__________________

Pelagic is online now   Reply With Quote
Reply

Tags
shore power

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Only one power cord is getting power from my shore power. Privilege Electrical: Batteries, Generators & Solar 10 11-09-2019 09:35
Portable Honda Gen to Shore Power- Can this power hot water electrics? simonpickard Electrical: Batteries, Generators & Solar 25 03-06-2019 08:30
Power Panel - Shore power light dmksails Electrical: Batteries, Generators & Solar 5 10-08-2017 11:02
Improving on Shore Power Connections Pelagic Electrical: Batteries, Generators & Solar 28 18-02-2015 12:03
Leopard 38: Shore Power Connections hikersailor Leopard Catamarans, Robertson & Caine 0 16-08-2014 17:48

Advertise Here


Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 05:36.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2019, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2019, vBulletin Solutions, Inc.
×

ShowCase vBulletin Plugins by Drive Thru Online, Inc.