Sizing and characterisctics of RCBOs & MBCs for 230V installation

[PaulRainbow]

The advice given is from a qualified electrical contractor, the o/p is dissing the advice, take the answer in context!

I'm a marine electrician. My advice to to follow the ISO in this matter, along with good, safe, practice. That is, fit an RCD close to the shore power inlet, before any equipment and in this case, before the isolation transformer.

Th OP claims he doesn't need to do that, because the shore power legal requirements absolve him of his responsibility to do so. This is clearly nonsense. All of us with shore power installations will have an RCD before our AC equipment, why don't we all stop fitting them and rely on the marina supply ? We all fit them because it is good practice and it protects our boats, our equipment and the people on our boats, irrespective of how good/bad the shore side systems are. The fact the OP plans to fit two after the isolator transformer is irrelevant, as that part of the installation is not protected by the shore power installation, it's all isolated by the transformer.

 

[lw395]

The representative of the boatyard mentioned appears to be agreeing with the OP and his penny pinching corner cutting of electrical safety

I'm not sure that is entirely fair.
An RCCB between the power inlet and the isolating transformer can only trip in very limited circumstances, such as the failure of the transformer itself, which is very unlikely.
But if there is any length of wiring between shore inlet and transformer, or reason that such wiring needs protection, I think it could be considered.
The whole area is a minefield.
There are multiple standards and methods.
Some standards for metal boats don't directly ground the neutral, it is grounded by a moderate impedance or an alarm sensor.
I don't believe that an isolating transformer necessarily removes the risk of galvanic corrosion BTW, or that it prevents the hull of the boat from having a different potential to shore metalwork.
I think, if I had a metal hulled boat with shore power, I'd be looking at the ground voltages and the common mode coupling across the transformer.

Bear in mind that some standards for ships work on the principle that it's better to electrocute the odd dirty matelot than to lose power to vital ship systems.
Whereas most standards for yachts take a more 'domestic' view. So there is conflict between standards.

 

[<152587>]

There comes a time, when good advice is given and argued against, then you have got to hold your hands up and say fine, do it your way and walk away. It appears that has been said in previous posts with no need to sleight reputation,

 

[matthewriches]

I'm glad I've managed to spice up an otherwise nonsense thread. VicS has shown his true colours, pot stirring again.

I've fitted many isolation transformers, i've worked with 30,000A motors, I fit equipment at the port of Felixstowe, I am qualified, insured and an freelance auditor and assessor for the largest commercial surveyor in Europe.

Just let the guy hear what he wants to hear. Easy.

If you work on a boat in a marina, you plug your extension lead in on the shore and throw it onto a boat..... you are relying on the shore power RCD or RCBO.

I've already given my professional opinion. As I stated in my previous post.... I fit them before and after transformers as that is what is required and what many ship insurers expect (not including some far east stuff I do).

Stay safe.

 

[lw395]

There comes a time, when good advice is given and argued against, then you have got to hold your hands up and say fine, do it your way and walk away. It appears that has been said in previous posts with no need to sleight reputation,

Well said.
There are more ways than one to skin a cat, as we usually don't have sight of the whole circumstances, most discussions on here can only hope to raise awareness of the pro's and con's of various systems.

 

[matthewriches]

Yup, forums used to be a good source of info sharing and discussion. Appears that a some on here seem to have a rather self-righteous status. My qualifications are available to view, as are up to date insurances and test equipment calibrations along with permits to work from the biggest shipping liners, tug companies, ports, etc, etc...

Shall we start to discuss RCD reliability?

Well said.
There are more ways than one to skin a cat, as we usually don't have sight of the whole circumstances, most discussions on here can only hope to raise awareness of the pro's and con's of various systems.

 

[Lon nan Gruagach]

Shall we start to discuss RCD reliability?

Ohh yes please.
And about how regular testing (you all do that don't you) reduces a minimal risk to a negligible one.

 

[Lomax]

Lol, this thread... What is it about the Internet that consistently prevents adult civilised discussion from taking place?

I'm not sure that is entirely fair. An RCCB between the power inlet and the isolating transformer can only trip in very limited circumstances, such as the failure of the transformer itself, which is very unlikely.

Oh good, so you do understand how this works. Yes, there will be a short length of cable between the shore intake and the isolation transformer. It will be less than two meters long, entirely above the waterline, "indoors" and well away from any sources of mechanical stress, and it will consist of a shielded installation cable with tinned conductors. I actually understand why one might fit an RCD & MCB or an RCBO on the primary side, and how this would increase the safety of the installation; not only in the event of a transformer fault, but also in case this short length of wire should be damaged in very specific ways (an RCD does not provide bulletproof protection, far from it!). But both these risks are only present while connected to a shore installation which lacks legally mandated protection. Now, I have to ask you, while it is possible to protect this short length of cable as described, what protects the 15 metres of 16A PVC cable between my boat and the pontoon outlet? A ten times longer cable, which is likely to experience far higher levels of mechanical stress and UV radiation, which may at times be wet, and which lacks the additional safety of an earth shield. A tiny nick in the insulation is all it would take to potentially kill the person handling it, should the marina have neglected to provide the legally required safety devices and make sure that these are functioning properly. And you guys are worrying about a 1.5m long cable which will never even be touched. Jeez. If this scenario is really keeping anyone up at night - which I seriously doubt - wouldn't the appropriate thing be to have an enclosure at the connecting end of the shore power cable wherein said RCBO is installed, right next to the pontoon outlet's own RCD?

I'd also like to add, that apart from the slanderous claims made against @matthewriches, I also take issue with the accusation that I am somehow "ignoring professional advice". This is unfair and incorrect - I listen to and I understand the advice I am given, and it's very much part of my decision making process. Do I therefore follow every bit of advice I am given? HELL NO! And neither do the loudmouths in this thread.

I'm done here, over and out.