2 RCDs?

[alexmh1985]

hi guys, i'm part way through the fit out of my new sailaway. I have the majority of the electrics in so far and just have a quick query regarding the RCD's. I have installed a Victron Multiplus 3000, and between this and the 240v ring I have installed an RCD with a 16amp breaker.

I have also installed a hull fitting for the shore power, my question is this, do I need to install an RCD between the shore power inlet and the Victron inverter/charger to protect it?

Thanks!

[WotEver]

Short answer - no. 

 

Longer answer - fit an RCD to the consumer unit, wire the shore input via IT or GI to the Multiplus, wire the Multiplus to the consumer unit. Run a bonding cable in 4mm² from consumer unit earth busbar to hull bonding point. Done. 

[Robbo]

A tip, install a galvanic isolator or isolation transformer, this would go between shore power inlet and the multiplus.

[alexmh1985]

brill, thanks for the speedy reply!

[nicknorman]

As said - no. Unless you have some other things powered direct from the shore power before it gets to the Combi. Some folk wire an immersion heater into the shore power before the Combi so it can only be powered from shore power and not from the inverter. But if you haven’t done that then just 1 RCD is needed.

 

Be aware of the max distance from shore power inlet to an overcurrent breaker as per ISO 13297 (compliance with which is required for the Rec. Craft Directive) is 0.5m, or 3m (measured along the length of the cabling) If the conductors are contained within protective covering.

[Sea Dog]

1 hour ago, alexmh1985 said:

and between this and the 240v ring 

Just a quick question:  Iirc, the 240V ring main is frowned upon in our application. Clearly it'll still work, but is it good practice?

[nicknorman]

23 minutes ago, Sea Dog said:

Just a quick question:  Iirc, the 240V ring main is frowned upon in our application. Clearly it'll still work, but is it good practice?

Not sure it’s frowned up, just that it’s not really necessary. Ring main in a house is a good thing because of the distances involved, number of sockets and max available current. In a boat the distances are usually less, fewer sockets and much less maximum possible current. No point.

[Richard10002]

2 hours ago, nicknorman said:

As said - no. Unless you have some other things powered direct from the shore power before it gets to the Combi. Some folk wire an immersion heater into the shore power before the Combi so it can only be powered from shore power and not from the inverter. But if you haven’t done that then just 1 RCD is needed.

 

 

I have a charger powered directly from the shore power, and an inverter charger also powered from the shore power. The boats 240v supply is powered from the inverter.

 

So I have 2 consumer units.

 

The reason for the second charger, is that, if shore power fails, the Sterling inverter charger switches to inverter, consuming 4A and potentially flattening the batteries.

 

A secondary bonus of the second charger is that it can be set to not revert to float charging long before the batteries are fully charged, which is useful if running a genny, and less so if on actual shore power.

[BruceinSanity]

10 hours ago, nicknorman said:

Be aware of the max distance from shore power inlet to an overcurrent breaker as per ISO 13297 (compliance with which is required for the Rec. Craft Directive) is 0.5m, or 3m (measured along the length of the cabling) If the conductors are contained within protective covering.

So in practice the answer is often yes, depending on the position of the inlet and the inverter/charger. If you have a second inlet in the bow, as we do, you need another breaker alongside that one.

[nicknorman]

24 minutes ago, BruceinSanity said:

So in practice the answer is often yes, depending on the position of the inlet and the inverter/charger. If you have a second inlet in the bow, as we do, you need another breaker alongside that one.

Yes but be careful, I am talking about the need for MCBs, not RCDs,

[WotEver]

1 hour ago, BruceinSanity said:

So in practice the answer is often yes...

No. As Nick explains above he referred to the RCD’s requirement for an MCB under certain circumstances, not an RCD. 

 

There are many and varied types of mains installations that are possible, my response was to the OP’s question regarding a single Multiplus plus shore power and I tried to keep the answer simple. 

[Robbo]

12 hours ago, nicknorman said:

As said - no. Unless you have some other things powered direct from the shore power before it gets to the Combi. Some folk wire an immersion heater into the shore power before the Combi so it can only be powered from shore power and not from the inverter. But if you haven’t done that then just 1 RCD is needed.

Note the multiplus has two outputs, one is for stuff like the immersion heater that’s only on when shore power is active.  Both outlets need a RCD.    It’s best to wire via the multi rather than before as the multi can adapt its charging rate so not to overload the shore power (or power assist)

[nicknorman]

Sure, if you use the other output, obviously that too needs an RCD and MCB. But I don’t think the OP has. And neither have I - I want to be able to run the immersion heater from internal power (engine running).

[Robbo]

22 minutes ago, nicknorman said:

Sure, if you use the other output, obviously that too needs an RCD and MCB. But I don’t think the OP has. And neither have I - I want to be able to run the immersion heater from internal power (engine running).

My multi which is quite old doesn’t have two outputs either.   I use a contactor to turn the “high loads” on/off so when my generator/shore is on it enables the high loads (only need one RCD as well).  This way the combi still sees the load so can adapt, etc.