Commercial dishwasher on a 32amp ring main

[JohnW2]

I was just gobsmacked that an electrician had no idea about fusing and non-fusing currents, even if he couldn't remember what the factors are for BS 1362 fuses.

Well, FWIW (given that I'm not an electrician), as I said, I can't remember them (probably because there is very rarely any need). Type B MCBs, yes, but BS1362 fuses, no.

So is the suggestion that someone who is not an electrician, and doesn't know what he's doing, is installing circuits in a public building? Which might also be a place of work?

That certainly seems to be the suggestion you are making - so, as I said, if you want to make a comment (or ask questions) about that, why not simply do so, rather than asking about recall of fuse operating characteristics? As I said, it seems to be unnecessary 'beating about the bush' - which, I have to say, is rather uncharacteristic of you

Kind Regards, John

 

[ban-all-sheds]

It is extremely uncharacteristic of me.

So...

Either I wasn't beating around the bush, and I meant just what I wrote, or I'd decided to go all cryptic.

You're an intelligent bloke - which do you think is more likely?

 

[JohnW2]

It is extremely uncharacteristic of me. So... Either I wasn't beating around the bush, and I meant just what I wrote, or I'd decided to go all cryptic. ... You're an intelligent bloke - which do you think is more likely?

I truly don't know - since you didn't make a statement which could 'mean what you wrote' - you asked a question. If your intention was to 'mean something' (rather than 'ask something'), I suppose that means that you were being fairly 'cryptic' (as you put it) by asking a question!

Kind Regards, John

 

[JohnD]

my memory isn't great, but AFAIR BS1362 fuses blow at 1.45 x rated value

I certainly can't remember time curves.

How near am I?

 

[JohnW2]

my memory isn't great, but AFAIR BS1362 fuses blow at 1.45 x rated value I certainly can't remember time curves. ... How near am I?

Not sure - I haven't bothered to look it up yet - but, apart from anything else, you'd have to qualify that statement with an indication of 'how fast blowing' you are talking about. The I2 of Type B MCBs is 1.45 x In - i.e. it is required to operate within 1 hour at a current which is 1.45 times its 'rated value' - is that perhaps what you are thinking of?

Kind Regards, John

 

[JohnD]

probably

 

[JohnW2]

probably

.... see the operating characteric curves for 3A and 13A BS1362s here .

From those curves, it looks as if it requires a current of about 40A (In x 3.08 ) to be sure of blowing a 13A fuse within 100 secs, about 26A (In x 2.00) to be sure of blowing it in 1000 secs (about 17 mins) and about 25A (In x 1.92) to be sure of blowing it in 4000 secs (a bit over 1 hour). However, the tolerances are quite large, and appreciably lower currents than those could result in blowing - down to about 22A (In x 1.69) for operation in 100 secs and about 21A (In x 1.62) for operation in 4000 secs.

... so, in general, it seems that it takes a fair bit more current to make a BS1362 fuse blow in a given time than would be required for a Type B MCB (of the same 'rating' {In}) to operate in the same amount of time.

Kind Regards, John

 

[ban-all-sheds]

PS - the above is not a claim that I am never insufficiently clear, or that I never explain myself properly.

It's a claim that there is never any artifice, there is never any deviousness, there are never any hidden meanings. If I think someone is a **#&%$£#~@ I will say so - lord knows I get told often enough that I mustn't, and that I must find a way to express that without being explicit.

So as for not explaining properly, above was an unfortunate example:

What I meant was that the whole idea that a 13A fuse might not blow as soon as you put more than 13A through it seemed a novel one to him.

I was trying to explain why I wrote what I did. I was trying to explain that I asked the question because I meant the question - "How come you're not aware of...". Note I did not ask "Why don't you know what I1 & I2 are for a BS 1362?"

My clumsy reply to JohnW2 was an attempt to explain why I asked it, that I couldn't understand why an electrician wouldn't know that there were such characteristics as I1 & I2. I didn't ask "Why don't you know what I1 & I2 are for a BS 1362?" because I don't expect people to know what the values are.

 

[ban-all-sheds]

I certainly can't remember time curves.

Nor can I, and whilst it would be fine if one could, I don't see anything wrong with not remembering. That's why we have published reference data.

my memory isn't great, but AFAIR BS1362 fuses blow at 1.45 x rated value

How near am I?

Unless Paul Cook is wrong, I1, or Inf if you prefer is 1.6In (with no time limit) and I2, or If is 1.9In (In his Commentary book there's also no time, so I assume it would be the conventional time of 1 hour.

So for a 13A fuse, I1 is 20.8A, and I2 is 24.7A

From those curves, it looks as if it requires a current of ... about 25A (In x 1.92) to be sure of blowing it in 4000 secs (a bit over 1 hour).

Also, from the curves, even the lower bound of a 13A BS 1362 goes vertical at just over 20A. 13 x 1.6 = 20.8.

 

[JohnW2]

Unless Paul Cook is wrong, I1, or Inf if you prefer is 1.6In (with no time limit) and I2, or If is 1.9In (In his Commentary book there's also no time, so I assume it would be the conventional time of 1 hour. ... So for a 13A fuse, I1 is 20.8A, and I2 is 24.7A

From those curves, it looks as if it requires a current of ... about 25A (In x 1.92) to be sure of blowing it in 4000 secs (a bit over 1 hour).

... It therefore seems as Mr Cook and my attempt to read from the curves I linked to are saying the same thing.

Also, from the curves, even the lower bound of a 13A BS 1362 goes vertical at just over 20A. 13 x 1.6 = 20.8.

Indeed so.

Kind Regards, John

 

[bwallum]

Well, DW now disabled, I won't take a current reading at present set up. Will re wire as radial first....maybe.

It appears this is a 3 phase designed DW (finally found a plate) that can be used as single phase. The 3 phase is applicable to the boiler elements (3 with separate contacts) giving 6kW (or should that be kVA) at 400v! The water pump is single phase rated at 755W, the tray heater element is single phase rated at 2.2kW, both the latter at 230v ac.

It appears that the fused spur was put in by an electrician on a 2.5mm2 T&E final ring circuit. I've found another identical fused spur running a fan. The cable from the fused spur to the below counter outlet is in 2.5mm2 T&E and probably fitted by the same electrician to a void, i.e. no machine present at time of installation. Protection to the ring is 32amp MCB/30maRCD (not rcbo as originally posted).

Perhaps later, a dishwasher was acquired and wired up to the undercounter outlet. The fuse popped after the heater had fired up and at the point the water pump kicked in.

4 years went by.

I was then asked to take a look at it and found that the machine worked without tripping the 32amp ring protection, but indeed would blow a 13 amp fuse.

So in addition we have to run a piece of 4mm2 T&E from above counter to under counter outlet as well as a 4mm2 dedicated radial service and disconnect the fused spur from the frc.

The 6kW water heater wired (by manufacturer) for a single phase works without tripping the 32amp protection.....but is it legal?

I guess it pulls less than the cooker (8 ring extra wide oven conventionally wired with it's own circuit )

 

[Spark123]

A heating element is a resistive load so KW is correct.

I don't understand your question regarding legality - it has been built for a commercial environment so is probably intended to have its own 32A or 30A supply, it possibly even came with a blue 32A ceeform plug on it.
Or are you questioning the legality of connecting it directly to a RFC via a 20A switch? If so then I'd say illegal as it hasn't been designed and constructed to minimise danger hence is a violation of section 4 of the EAWR.

Cookers can have diversity applied, thermostats turn on/off so are not pulling full power constantly, you also don't tend to run everything at the same time.

 

[bwallum]

I would have liked to have shown you the full manual, absolute nightmare, but it was 6.5 Mbytes and the upload limit is 6. I have selected a very few pages that may answer the 'have you got' questions. The model number again is CK50/ABS/DD, the ABS refers to Air Break System, the DD means direct drain (no pump) and the CK50 means a big b----r apparently.

ABS model specific components

Untitled

• bwallum
• 23 Aug 2014
• 1

Image showing 6kW heater as 3 phase model

Untitled

• bwallum
• 23 Aug 2014
• 1

Single phase boiler element which would have made sense but not fitted on the single phase ABS model

Untitled

• bwallum
• 23 Aug 2014
• 1

This image shows single phase flexible 6mm2 x 3 input cable

Untitled

• bwallum
• 23 Aug 2014
• 1

This image shows the 3 loops boiler element

Untitled

• bwallum
• 23 Aug 2014
• 1

 

[ban-all-sheds]

I truly don't know - since you didn't make a statement which could 'mean what you wrote' - you asked a question. If your intention was to 'mean something' (rather than 'ask something'), I suppose that means that you were being fairly 'cryptic' (as you put it) by asking a question!

Well - as it seems that someone has decided that I may not explain, and may not make clear the vital importance of people reading what I write, you and others like you are going to remain ignorant. As a result we will keep on having problems when those who have not grasped the importance of simply reading what I write decide to invent stuff and then criticise me when they find they don't like what they've just invented.

 

[bwallum]

er...how about this weird dishwasher?

Looks as though it was designed as a 3phase, then modified to a single phase, giving a much higher current demand in the process. Are such commercial dishwashers usual?