Type AC, B or F RCD for boats?

[jdc]

Following on from the Garage Consumer Unit thread, I've been wondering for some time about the changing electrical loads boats now impose on the mains supply. There are no regs as such, but I'd like to follow good practice nonetheless, essentially complying with IET edition 18.

RCDs / RCCBs come in various types according to the expected loads. The old type AC devices are no longer considered suitable where there is mains-powered LED lighting or induction ovens or other inverter or switching loads. And for my electric car I had to install a type B.

It strikes me that modern battery chargers and immersion heaters will almost inevitably be inverters / switching devices, especially if there are lot of Lithium batteries on board, so would anyone now recommend installing a type F?

Similarly for MCBs, there are classes B, C and D. Class C is easiest to source, but may not be appropriate on a boat: it's the threshold for instantaneous tripping which is the difference between the types:

Type B - trips between 3 and 5 time full load current
Type C - trips between 5 and 10 times full load current
Type D - trips between 10 and 20 times full load current

If I were doing a new install, I think I'd go for a type F RCD, and type B MCBs, but what do others think reasonable? Presumably it depends on the loads.

 

[Alex_Blackwood]

Following on from the Garage Consumer Unit thread, I've been wondering for some time about the changing electrical loads boats now impose on the mains supply. There are no regs as such, but I'd like to follow good practice nonetheless, essentially complying with IET edition 18.

RCDs / RCCBs come in various types according to the expected loads. The old type AC devices are no longer considered suitable where there is mains-powered LED lighting or induction ovens or other inverter or switching loads. And for my electric car I had to install a type B.

It strikes me that modern battery chargers and immersion heaters will almost inevitably be inverters / switching devices, especially if there are lot of Lithium batteries on board, so would anyone now recommend installing a type F?

Similarly for MCBs, there are classes B, C and D. Class C is easiest to source, but may not be appropriate on a boat: it's the threshold for instantaneous tripping which is the difference between the types:

Type B - trips between 3 and 5 time full load current
Type C - trips between 5 and 10 times full load current
Type D - trips between 10 and 20 times full load current

If I were doing a new install, I think I'd go for a type F RCD, and type B MCBs, but what do others think reasonable? Presumably it depends on the loads.

I would use TYPE "A" RCD and CURVE "B" MCB or equivalent RCBO. That will give all you need in the way of protection on a boat. No reason why you cannot use "F" or "B" RCD if you feel happier. All a bit of how you toss the coin. They will all protect, of course, and yes you are right when you say it depends on the loads. Every case, every installation needs individual consideration. I am not sure where you get the inverter association with immersion heaters. A normal battery charger will be most probably be some sort of Switch mode rectification and control, unless of course you are talking combined charger inverters. (Don't get confused with rectification and inversion)
All in all at the end of the day it will depend on your installation, personal choice, and possibly depth of pocket
Good question though and does need some thought in the modern world.

 

[Boater Sam]

Curve "D" MCBs are called never trips in the trade!
I have never had any problems with "AC" RCDs on boats with LED mains voltage lighting and inverters.

 

[Alex_Blackwood]

Curve "D" MCBs are called never trips in the trade!
I have never had any problems with "AC" RCDs on boats with LED mains voltage lighting and inverters.

You won't know you have a problem with TYPE "AC" until it doesn't trip under fault because of a statured operating coil. Even then you may not know of the problem because you will be dead

 

[jdc]

My thoughts about DC currents exactly, which prompted my original question.

The Inverter reference was in the IET wiring regs book, which I guess might be inverters from EV or battery walls so not exactly what we have aboard (I assume). But nonetheless, the input to almost all mains electronics these days starts with full-wave rectification and then a fairly high frequency switch-mode stage (in the range 30kHz to 1MHz I guess), and then either via a galvanic isolator - ie a ferrite transformer - or, more dangerous for humans if they touch it - direct to the load. Your computer power brick the former, immersion heaters are, I fear, usually the latter.

Old ones had a simple bang-bang controller, probably just a bi-metallic thermostat, as did fridges, but modern ones tend to use more variable control (which might well be DC) or variable speed compressors via brushless motors. So I think there's a strong possibility of DC currents flowing under earth fault conditions. Type A is a good steer 'tho.