What is this - an external isolator?

[JohnW2]

John. My interpretation of this post says you are totally contradicting yourself.

Not at all. The difference between us results from our very different views about relative risks (risks wich our practices {be they 'best' or whatever} seek to mitigate/minimise).

Initially you are advocating botching by not being be arsed to bother to install any sort of earth connexion in contravention of 'best practice' or MI's and presumably dumping the items supplied in the gland pack in the scrap metal bag....

I can only talk of my personal views and practices, but I obviously do not regard it as 'botching' etc.

Next you advocate doubling up on the IP rating by spending a lot of money on a totally unneccessary and larger enclosure.

The explanation for my different personal views in those two situations results from my different (personal) views about the 'risks' involved. Despite the extreme anecdotal experiences you are able to cite, I regard the probability of the absence of a banjo in a metal box ever giving rise to a problem as being incredibly small, whereas I regard (through experience) the probability of water ingress into an allegedly IP66 accessory which is 'totally exposed to the elements' to be much higher than that 'incredibly small' probability.

Please do me a favour and stop saying the banjo [or some other item] to provide electrical continuity is not required. Simply adding a lockring in a metal box may work for the initial testing but it is far from the reliable solution you seem to think it is.

In the case of a (galvanised, plated or stainless) steel box, all you seem to be proposing is to bolt a bit of brass in parallel with the steel which would provide the electrical path from gland body to CPC lugs without the brass, using the same gland nut and nut/bolt as you would do without the brass. Other than for the different metals (which you have agreed is not an issue), I don't see that achieving anything significant. If (per some of your extreme anecdotes) the steel rusts/disintegrates to the extent that electrical continuity is lost, I image that it very likely (probably nearly inevitable) that the mechanical, and hence also electrical, connection to the brass will also have suffered (maybe even 'failed').

Of course, if the box is plastic, painted or otherwise coated with something non-conductive, then one has no choice but to use a banjo - but that's not what we are talking about.

Given that we appear to be talking about extremely rare theoretical 'risks', it's probably worth noting that there are also theoretical 'downsides' of using banjos when they are not necessarily 'required'. Particularly when marked thermal cycling is a possibility, bolting together sandwiches of different materials can (due to differential expansion/contraction of the different materials) make it more likely that things will 'work loose'. A very small risk, I'm sure, but not necessarily smaller than some of the 'risks' you are considering. I don't know whether there are any possible electrochemical issues at the interface between brass and (galvanised/whatever) steel, but it wouldn't surprise me if there were. Edit: In fact, having had a quick conversations with Mr Google, the first hit he provided (click here) seems to suggest that there is a potential problem, where it says ....

... but if brass and steel contact, the steel will corrode because it is more anodic than the brass.

Kind Regards, John

 

[Harry Bloomfield]

As Rocky said, one could put a CU (or any other sort of 'distribution equipment') in a suitable outdoor enclosure, but I'm not sure that I would really want even that - and, as I said, I can't recall having seen such in any UK domestic garden - have you?

Go on any touring caravan site and you will find small CU's scattered about the place, some with several ways involved.

 

[davelx]

Go on any touring caravan site and you will find small CU's scattered about the place, some with several ways involved.

And any marina too - surrounded by salt water.

 

[JohnW2]

What I can't fathom is what the fundamental difference is between steel conduit and SWA? it seems to be the "done thing" to use banjos with SWA but not with steel conduit.

Quite. I think the reason you can't "fathom ... what the fundamental difference is" is that there is NO fundamental (if any!) difference!

Kind Regards, John

 

[JohnW2]

Go on any touring caravan site and you will find small CU's scattered about the place, some with several ways involved.

And any marina too - surrounded by salt water.

I don't frequent such places (I did say that 'my experience is limited) but do not doubt that what you say is true. However, as I've said, I must have seen hundreds of domestic gardens in my time, and don't recall having seen an 'exposed' CU in any of them - but that obviously doesn't necessarily mean that they don't exist.

Does anyone have any idea how common it is for there to be problems of water ingress in any of these things in caravan sites and marinas?

Kind Regards, John

 

[JohnW2]

It certainly used to be the way but as the conduit ages the joints become less reliable.

Are you suggesting that as a reason for, or against, the use of banjos with conduit?

Kind Regards, John

 

[SUNRAY]

In the case of a (galvanised, plated or stainless) steel box, all you seem to be proposing is to bolt a bit of brass in parallel with the steel which would provide the electrical path from gland body to CPC lugs without the brass, using the same gland nut and nut/bolt as you would do without the brass.

Oh no I certainly do not propose adding a 'bit of brass' in parallel with the steel.
What I propose, and do, is make a secure connexion between the gland and the earth requirements of the accessory.
Securing the banjo between 2 brass nuts, and never just a single nut and certainly not steel, provides a degree of mechanical isolation from the mechanical joint with the enclosure.
It could very well happen to appear to be the same as bridging the mechanical [and not electrical] joint with the enclosure

Other than for the different metals (which you have agreed is not an issue), I don't see that achieving anything significant.

I have not agreed dissimilar metals are not an issue. In fact all the way through I've been saying the opposite.

If (per some of your extreme anecdotes) the steel rusts/disintegrates to the extent that electrical continuity is lost, I image that it very likely (probably nearly inevitable) that the mechanical, and hence also electrical, connection to the brass will also have suffered (maybe even 'failed').

My anecdotes are descriptions of real life experiences and I'll say is representative of a number of tens of situations. The assumption the electrical connexion would have been lost as well is unfounded and inappropriate in a very high percentage of those cases. Chances are the brass may have verdigre on it but the likelyhood is the brass banjo securely clamped between 2 brass nuts onto the brass thread would still retain a reasonable electrical connexion.

Of course, if the box is plastic, painted or otherwise coated with something non-conductive, then one has no choice but to use a banjo - but that's not what we are talking about.

The materials matter not, there is no reason to downgrade the procedure when all the parts are provided in the kit.

Given that we appear to be talking about extremely rare theoretical 'risks',

Again you missunderstand me, I'm refering to very real situations, very real, a single report from a customer of "Electric shock when I touch the switch" is one too many and I've lost count of the number of times that report, or something fairly similar, is correct.

it's probably worth noting that there are also theoretical 'downsides' of using banjos when they are not necessarily 'required'. Particularly when marked thermal cycling is a possibility, bolting together sandwiches of different materials can (due to differential expansion/contraction of the different materials) make it more likely that things will 'work loose'. A very small risk, I'm sure, but not necessarily smaller than some of the 'risks' you are considering.

Where is this happening when "the brass banjo securely clamped between 2 brass nuts onto the brass thread"?

I don't know whether there are any possible electrochemical issues at the interface between brass and (galvanised/whatever) steel, but it wouldn't surprise me if there were. Edit: In fact, having had a quick conversations with Mr Google, the first hit he provided (click here) seems to suggest that there is a potential problem, where it says ....

... but if brass and steel contact, the steel will corrode because it is more anodic than the brass.

Surely another good reason to not rely on the junction between a brass gland and a steel enclosure!

Kind Regards, John

Again I struggle to understand your comments as initially you say dissimilar metals don't matter then post links to say it does matter.

I will add that the banjo was very successfully in use for many years, all the time we had conscientious people doing this sort of work, with the very casual attitude of so many now other solutions have had be found and the earth nut very closely duplicates the correct application of the banjo where there is no reliance on the mechanical joint between the gland and enclosure.

 

[SUNRAY]

Are you suggesting that as a reason for, or against, the use of banjos with conduit?

Kind Regards, John

Well I dont rely on conduit for an earth connexion, does that answer the question adequately?

 

[SUNRAY]

I don't frequent such places (I did say that 'my experience is limited) but do not doubt that what you say is true. However, as I've said, I must have seen hundreds of domestic gardens in my time, and don't recall having seen an 'exposed' CU in any of them - but that obviously doesn't necessarily mean that they don't exist.

Does anyone have any idea how common it is for there to be problems of water ingress in any of these things in caravan sites and marinas?

Kind Regards, John

It's not a common issue otherwise it would have been done away with.

 

[JohnW2]

Well I dont rely on conduit for an earth connexion, does that answer the question adequately?

Not really, no. At least in the past, plenty of people did rely on it, but do you think they should have used a banjo (made of what material, I wonder?) when it connected to a metal box?

Kind Regards, John

 

[JohnW2]

It's not a common issue otherwise it would have been done away with.

Hmmm. I've heard that one in many contexts

Kind Regards, John

 

[JohnW2]

I have not agreed dissimilar metals are not an issue. In fact all the way through I've been saying the opposite.

....

My belief is the earth lead to the gland body has nothing to do with dissimilar metals.

Kind Regards, John

 

[JohnW2]

Oh no I certainly do not propose adding a 'bit of brass' in parallel with the steel.

As I understand it, you effectively are (electrically) are ...

What I propose, and do, is make a secure connexion between the gland and the earth requirements of the accessory. Securing the banjo between 2 brass nuts, and never just a single nut and certainly not steel, provides a degree of mechanical isolation from the mechanical joint with the enclosure.

Yes, if one does that (which I suspect a good few don't), and particularly if one uses three nuts (which I imagine even less people do), then the two mechanical joints will be (mechanically) 'isolated' from one another.

However, that does not alter the fact that if all the joints are mechanically (hence also electrically) sound, that there will then be an electrical path through the steel in parallel with that through the brass (or vice versa, if one wants to look at it like that).

Kind Regards, John

 

[JohnW2]

... but if brass and steel contact, the steel will corrode because it is more anodic than the brass.

Surely another good reason to not rely on the junction between a brass gland and a steel enclosure!

... or, looked at another way, a good reason for not unnecessarily introducing brass into the equation?

Kind Regards, John

 

[SUNRAY]

... or, looked at another way, a good reason for not unnecessarily introducing brass into the equation?

Kind Regards, John

Surely it would make more sense to not introduce ferrous metals into the equasion, would it not?

Ever wondered why mineral insulated cable is made of... oo let me see...