Looking to install a 3ph supply for 2 x 6kW fryer in a commercial kitchen.

[James.B]

Hi everyone, I've looked at a job to install a circuit for a 2x 6kW fryer in a commercial kitchen and would really appreciate a second opinion on my calcs, attached in photos. Many thanks in advance.

 

[timbobelfast]

Looks OK, 6mm for me as the cost between 4 and 6 is negligible. Allows for future expansion and if terminals cable of taking 6mm. Also may consider omitting RCD

 

[plugsandsparks]

Haven't look at the calcs but if you can get two ccts in, rather than try and run two off one cct, its always better in the long run.
You can run 2 X 2.5sqmm 4 core terminate on two Rotary isolaters and put on a B16 breaker, almost impossible for that not to work (subject to calcs again. Lol
Biggest issue with a C32 is ELI

 

[Ian1981]

Do not base the ccc of the cable on 90 degree operating temperature, use the tables for Swa at a 70 degree operating temperature as the mcb and other terminals will not be rated for 90 degrees.

 

[James.B]

Thanks timbo, I appreciate your swift reply?. I thought the same about 6mm cable just to be on the safe side, but it is less than a 15m run and clipped direct and 4mm is capable of 42A installed like this, and we all know there should be plenty of buffer built in even at that, given the draw is less than 17.5Amps per phase. It's just one of those things where you'd like to be safe, it's just nice to get a second opinion sometimes as we all second guess ourselves sometimes, maybe its the beer??. Thanks again mate

 

[davesparks]

4mm is capable of 42A installed like this,

Is that the 90C rating or 70C rating?

Also if Ib is 17.3A then surely In would be 20A?

 

[James.B]

Haven't look at the calcs but if you can get two ccts in, rather than try and run two off one cct, its always better in the long run.
You can run 2 X 2.5sqmm 4 core terminate on two Rotary isolaters and put on a B16 breaker, almost impossible for that not to work (subject to calcs again. Lol
Biggest issue with a C32 is ELI

Thanks plugs and sparks, the fryer hasn't been purchased yet as I'm told it comes as a single or 3ph option, I done calcs for both but obviously best to install 3ph when you have the option as cable size for single phase comes in at 10mm. So not sure about terminal sizes etc. Could you go into more detail about your proposal please, just interested, thanks again for speedy reply?

 

[davesparks]

Haven't look at the calcs but if you can get two ccts in, rather than try and run two off one cct, its always better in the long run.
You can run 2 X 2.5sqmm 4 core terminate on two Rotary isolaters and put on a B16 breaker, almost impossible for that not to work (subject to calcs again. Lol
Biggest issue with a C32 is ELI

How on earth can you connect a single appliance to 2x circuits safely?

 

[James.B]

Do not base the ccc of the cable on 90 degree operating temperature, use the tables for Swa at a 70 degree operating temperature as the mcb and other terminals will not be rated for 90 degrees.

Thanks Ian, point noted, therefore multicore armoured @ 70 C is 33A for a 4mm cable, maybe I will go for the 6mm in that case as that states 42A ref method C. Appreciate your input mate?
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Is that the 90C rating or 70C rating?

Also if Ib is 17.3A then surely In would be 20A?

It's the 90C rating mate, but as Ian quite rightly pointed out @70 C it carries 33A on 4mm cable, so possibly will use 6mm. I'm installing it for this piece of equipment on a 32A commando with build in rotary isolator and rcd just in case of future use for something else. Also the DB is a discontinued Crabtree Polestar 125A, hence the reason for the 2 in one socket. Cheers
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How on earth can you connect a single appliance to 2x circuits safely?

I wondered that too Dave sparks, that's why I politely asked to explain in more detail?

 

[davesparks]

It's the 90C rating mate, but as Ian quite rightly pointed out @70 C it carries 33A on 4mm cable, so possibly will use 6mm. I'm installing it for this piece of equipment on a 32A commando with build in rotary isolator and rcd just in case of future use for something else. Also the DB is a discontinued Crabtree Polestar 125A, hence the reason for the 2 in one socket. Cheers

That still doesn't explain why you've selected a 32A OCPD for a 17.3A load when 20A would be the more logical choice?

 

[plugsandsparks]

How on earth can you connect a single appliance to 2x circuits safely?

2 X 6KW fryer = 2 X 6kw fryer = 2 appliances otherwise it would be 1 X 12KW fryer.
You need to take a chill pill, its hard enough deciphering half this stuff without you adding to it

 

[davesparks]

2 X 6KW fryer = 2 X 6kw fryer = 2 appliances otherwise it would be 1 X 12KW fryer.
You need to take a chill pill, its hard enough deciphering half this stuff without you adding to it

I assume from the fact the OP has seen the spec for the appliance and is designing it as a single supply that a 2x6kW fryer is a single appliance comprising of 2 fryers, each rated at 6kW.

The language in the OP is quite clear "A circuit for A 2x6kW fryer" if it was indeed 2 appliances the OP would use the plurals, "circuits for 2x6kW fryers"

 

[timbobelfast]

That still doesn't explain why you've selected a 32A OCPD for a 17.3A load when 20A would be the more logical choice?

32A would be my preference, the circuit is 15m long so EFLI not going to be an issue here.
No point loading up a 20A TP MCB, he's also stated that the board and mcbs are obsolete and that he had a 32A MCB. Ccc also not an issue after correction factors applied.

 

[Vortigern]

For what it's worth I did a 3 Phase oven and calculated 2.5 and the manufacturer insisted they always use 4mm. Maybe the manufacturer of the fryers might have some input? I suppose as it is a cafe they do tend to run their appliances at full tilt for much of the day so yeh belt and braces approach.

 

[James.B]

That still doesn't explain why you've selected a 32A OCPD for a 17.3A load when 20A would be the more logical choice?

I agree with you Dave sparks, my apologies I'm not fully up to speed with calcs as being honest I haven't done any in about 20yrs, as all large scale jobs I worked on had designers, so excuse my ignorance. Initially I had drawn up calcs for a 20A breaker but was advised by a designer to up it to 32 A and use a 2 in 1 socket, photo attached. Would you mind me asking for your personal opinion please

 

[plugsandsparks]

I assume from the fact the OP has seen the spec for the appliance and is designing it as a single supply that a 2x6kW fryer is a single appliance comprising of 2 fryers, each rated at 6kW.

The language in the OP is quite clear "A circuit for A 2x6kW fryer" if it was indeed 2 appliances the OP would use the plurals, "circuits for 2x6kW fryers"

I will bow to the forums use of english, i could equally have assumed the OP missed off the S but struggling with why it would be described as 2 X 6KW and not 1 X 12KW, so i had assumed he only had one cct, hey ho

 

[timbobelfast]

I agree with you Dave sparks, my apologies I'm not fully up to speed with calcs as being honest I haven't done any in about 20yrs, as all large scale jobs I worked on had designers, so excuse my ignorance. Initially I had drawn up calcs for a 20A breaker but was advised by a designer to up it to 32 A and use a 2 in 1 socket, photo attachedView attachment 59723. Would you mind me asking for your personal opinion please

Nothing wrong with a 32A OCPD lad, cable Ccc OK, EFLI likely to be well under the max.
If this is going to running for 12 - 15 hours a day, a 32A MCB will operate at a cooler temp than a 20A MCB in this environment.

Your the designer at the end of the day!

 

[davesparks]

I will bow to the forums use of english, i could equally have assumed the OP missed off the S but struggling with why it would be described as 2 X 6KW and not 1 X 12KW, so i had assumed he only had one cct, hey ho

For me that is a perfectly normal way to describe the power rating of something, I see a lot of equipment with ratings like that. For example I install stage lighting dimmers described as 12x2.4kW or 24x2.4kW, these are single pieces of equipment which have 12 or 24 channels of 2.4kW dimmers.

Or a 2x13A socket is not 2 seperate items, it's a single plate with 2 bs1363 sockets on it, it's also not a 26A socket.

 

[James.B]

2 X 6KW fryer = 2 X 6kw fryer = 2 appliances otherwise it would be 1 X 12KW fryer.
You need to take a chill pill, its hard enough deciphering half this stuff without you adding to it

Sorry plugs and sparks, I wasn't clear in my description, this is a twin fryer but 1 single piece of equipment, that is why I asked for you to explain, no offence intended. These fryers can be used individually or both together and come in both single and a 3ph option.

 

[plugsandsparks]

For me that is a perfectly normal way to describe the power rating of something, I see a lot of equipment with ratings like that. For example I install stage lighting dimmers described as 12x2.4kW or 24x2.4kW, these are single pieces of equipment which have 12 or 24 channels of 2.4kW dimmers.

Or a 2x13A socket is not 2 seperate items, it's a single plate with 2 bs1363 sockets on it, it's also not a 26A socket.

Interesting.. I would never describe a double socket as a 2 X13A socket, that would be 2 X single gang sockets. It would be interesting when the fryer shows up what the rating plate says.... please OP take a pic.... it might make my day ( or not) lol

 

[James.B]

That still doesn't explain why you've selected a 32A OCPD for a 17.3A load when 20A would be the more logical choice?

Hey Dave, I have selected a 32A incase it could be used for another piece of equipment in the future, if I limit it to 20A this may not be sufficient for future use. Cheers

 

[plugsandsparks]

Sorry plugs and sparks, I wasn't clear in my description, this is a twin fryer but 1 single piece of equipment, that is why I asked for you to explain, no offence intended. These fryers can be used individually or both together and come in both single and a 3ph option.

No sweat, just enjoying the joy of eletricary, 3PH is good if you can wire it that way when it arrives. As mentioned before C32 earth loop is what i would concentrate on for design, if you take a ZDb before you order the cable, it might help with sizing, alternatively drop to a C25 or even a B32.

 

[James.B]

Nothing wrong with a 32A OCPD lad, cable Ccc OK, EFLI likely to be well under the max.
If this is going to running for 12 - 15 hours a day, a 32A MCB will operate at a cooler temp than a 20A MCB in this environment.

Your the designer at the end of the day!

Agreed Timbo, as I said initially I was designing it solely for this piece of equipment but then advised to up it for the extra scope for future and so I did, I was just interested to get other people's opinions on here and obviously double check myself as it's been yrs since I've done calcs, so really appreciate your input mate?
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Interesting.. I would never describe a double socket as a 2 X13A socket, that would be 2 X single gang sockets. It would be interesting when the fryer shows up what the rating plate says.... please OP take a pic.... it might make my day ( or not) lol

I will mate?
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Many thanks to everyone for their help, much appreciated guys?

 

[James.B]

32A would be my preference, the circuit is 15m long so EFLI not going to be an issue here.
No point loading up a 20A TP MCB, he's also stated that the board and mcbs are obsolete and that he had a 32A MCB. Ccc also not an issue after correction factors applied.

Thanks again Timbo, I somehow seem to have missed this post last night?
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For what it's worth I did a 3 Phase oven and calculated 2.5 and the manufacturer insisted they always use 4mm. Maybe the manufacturer of the fryers might have some input? I suppose as it is a cafe they do tend to run their appliances at full tilt for much of the day so yeh belt and braces approach.

Sorry Vortigern, I seem to have missed this post last night too?‍. The fryer is a Parry and customer wants to purchase from Nesbitts, you were lucky to get to speak to technical, I tried twice to both Parry and Nesbitts, no one to help and no one phoned back after they said they would so?‍. Totally agree with the belt and braces approach and am guilty of over specing so good to have a mixture of tabulated figures to go by but also to be able to touch base with people who have more experience in this particular field than myself (Commercial Kitchens). Many thanks for your input.

 

[telectrix]

and as a fixed load, overcurrent protection is not required, so 32A MCB is ideal as long as In<Iz.

 

[Ian1981]

and as a fixed load, overcurrent protection is not required, so 32A MCB is ideal as long as In<Iz.

You mean Ib is equal to or less than Iz
The protective device can exceed the Iz of the cable where overload protection is not required as long as the design current is equal to or less than Iz.

 

[telectrix]

You mean Ib is equal to or less than Iz
The protective device can exceed the Iz of the cable where overload protection is not required as long as the design current is equal to or less than Iz.

sorry. i should have said Ib<Iz. what idiot put N next to B on my keyboard. just almost as bad as the caps lock next to A, so every time my fat sausage fingres type an a, EVERYTHING AFTER IS CAPS.

 

[Ian1981]

sorry. i should have said Ib<Iz. what idiot put N next to B on my keyboard. just almost as bad as the caps lock next to A, so every time my fat sausage fingres type an a, EVERYTHING AFTER IS CAPS.

I forgive you, can’t help with the keyboard situation, i always use my iPhone, spell check is a godsend ha.

 

[telectrix]

corrective text is a pain. once i had a customer of far east origin, name is Alka. i sent her a text which started as Hi AklaSeltzer.

 

[pc1966]

No sweat, just enjoying the joy of eletricary, 3PH is good if you can wire it that way when it arrives. As mentioned before C32 earth loop is what i would concentrate on for design, if you take a ZDb before you order the cable, it might help with sizing, alternatively drop to a C25 or even a B32.

As a fryer presumably has no switch-on surge of any note (maybe small motor for oil circulation?) I don't see any reason for a C-curve MCB and the B-curve version will make the required Zs far easier to meet.

 

[James.B]

Thanks Ian and Telectrix, yes my In is greater than my Ib and my Iz is greater than my In. If I used 4mm cable as mentioned before, my It would not be greater than my Iz using the 70 deg C tables, but i believe this (condition 3) unessary to meet once condition 1 & 2 are met. In saying that, I now plan to use a 6mm cable anyway therefore my It will be greater than my Iz. I see many people have mentioned about not protecting by an RCD, but I believed this was only the case where the RCD was nigated by a Risk assessment (411.3.3), personally I would prefer to fit one and would not nigated it. But would you be so kind as to maybe give reference to where the regs states this if other than by a Risk assessment? Many thanks, James?

 

[Ian1981]

Thanks Ian and Telectrix, yes my In is greater than my Ib and my Iz is greater than my In. If I used 4mm cable as mentioned before, my It would not be greater than my Iz using the 70 deg C tables, but i believe this (condition 3) unessary to meet once condition 1 & 2 are met. In saying that, I now plan to use a 6mm cable anyway therefore my It will be greater than my Iz. I see many people have mentioned about not protecting by an RCD, but I believed this was only the case where the RCD was nigated by a Risk assessment (411.3.3), personally I would prefer to fit one and would not nigated it. But would you be so kind as to maybe give reference to where the regs states this if other than by a Risk assessment? Many thanks, James?

411.3.3 is the regulation you want for omission of additional protection by a risk assessment

 

[telectrix]

Thanks Ian and Telectrix, yes my In is greater than my Ib and my Iz is greater than my In. If I used 4mm cable as mentioned before, my It would not be greater than my Iz using the 70 deg C tables, but i believe this (condition 3) unessary to meet once condition 1 & 2 are met. In saying that, I now plan to use a 6mm cable anyway therefore my It will be greater than my Iz. I see many people have mentioned about not protecting by an RCD, but I believed this was only the case where the RCD was nigated by a Risk assessment (411.3.3), personally I would prefer to fit one and would not nigated it. But would you be so kind as to maybe give reference to where the regs states this if other than by a Risk assessment? Many thanks, James?

how will the fryers be connected? hard wired or on plug? and will cable be buried <50mm in wall?

 

[plugsandsparks]

As a fryer presumably has no switch-on surge of any note (maybe small motor for oil circulation?) I don't see any reason for a C-curve MCB and the B-curve version will make the required Zs far easier to meet.

I think the only issue i can see is getting TP B curve breakers for that board, TBH its getting harder and harder to meet ELI with the values dropping as they do. Did an EICR on an office ring that was put in 10 years ago on a c32, failed today just outside ELI, its a MEM board , nothing wrong with the cct, hey ho

 

[James.B]

As a fryer presumably has no switch-on surge of any note (maybe small motor for oil circulation?) I don't see any reason for a C-curve MCB and the B-curve version will make the required Zs far easier to meet.

Hi PC, the reason for me using C Type 32 was because I have one, and the DB is the old Crabtree Polestar 125A, discontinued about 10 yrs ago, but point noted and I agree. With a Ze of 0.1 on a TN-C-S and using a 4 core 6mm swa using the armour as my cpc cleated direct on a run of less than 15m I'd expect a pretty decent Zs, sub 0.2, so hopefully no foreseeable issues and will also be RCD protected, cheers James?
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411.3.3 is the regulation you want for omission of additional protection by a risk assessment

Thanks Ian I thought that was the only reg alright, appreciate your time mate?

 

[marconi]

JamesB: I admire the care you are taking with the required analysis and that you record it too ( - I assume) for posterity - just in case. Well done , Sir.

Plenty of great advice from some leading runners in the game.

Did your client consider 'induction fryers'? A lot more efficient and quicker.

Induction Fryers, Buy Online UK | Nisbets Induction Cooking Machines - https://www.nisbets.co.uk/catering-appliances/cooking-equipment/induction-cookers/induction-fryers/_/a33-4

View: https://www.youtube.com/watch?v=7GcMRCUw2J0


I recommended 2 x 3kW to my brother-in-law to make best use of a very limited single phase power supply to cook chips at football ground catering van.

 

[James.B]

how will the fryers be connected? hard wired or on plug? and will cable be buried <50mm in wall?

Hi Telectrix, fryers will be wired via a 32A 5 pin plug and socket, with rotary interlock switch and RCD protected. Using a 4 core 90 deg thermosetting swa cleated direct and with pirana locking nuts. With the rotary isolator being of plastic construction I'll gland into a metal J.Box first and into the isolator from that, unless there's a better option on the market these days that I don't know about??? Open to other options, and appreciated, many thanks?

 

[telectrix]

if the 32A socket is dedicated to the fryer, my thoughts are that RCD may not be required. A written RA might be advisable.

 

[James.B]

JamesB: I admire the care you are taking with the required analysis and that you record it too ( - I assume) for posterity - just in case. Well done , Sir.

Plenty of great advice from some leading runners in the game.

Thank you Marconi, yes some good advice from people that I appreciate, to be able to so called, bounce off, things change so quickly in this industry and it's good to be able to come on here and if you have an issue or a doubt, then put it out there. As they say that's what this forum is all about, and everyday is a learning day, none of us know everything and sometimes can even forget our basics no matter how much experience we have?. A guy said to me many years ago, cover your --- and sign any legal document as if you are standing in a court of law. I guess old habits die hard ?. Appreciate your feed back, thanks James?
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if the 32A socket is dedicated to the fryer, my thoughts are that RCD may not be required. A written RA might be advisable.

It is dedicated to the fryer, at this moment in time, the problem is I know the owner and I also know he changes his mind like the wind and it may be used for something else in the future, therefore I'd prefer to cover my --- as they say, I know there is the cost element, but that's on him and I walk away with a clear conscience knowing all is well. In saying that I appreciate your informative info, many thanks again?
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JamesB: I admire the care you are taking with the required analysis and that you record it too ( - I assume) for posterity - just in case. Well done , Sir.

Plenty of great advice from some leading runners in the game.

Did your client consider 'induction fryers'? A lot more efficient and quicker.

Induction Fryers, Buy Online UK | Nisbets Induction Cooking Machines - https://www.nisbets.co.uk/catering-appliances/cooking-equipment/induction-cookers/induction-fryers/_/a33-4

View: https://www.youtube.com/watch?v=7GcMRCUw2J0


I recommended 2 x 3kW to my brother-in-law to make best use of a very limited single phase power supply to cook chips at football ground catering van.

Thanks Marconi, I did see these when I was looking up the fryer he speced, I'm sure he's seen them but seems adamant about this particular one, another reason why I speced a 32 breaker instead of what would have been a 20 for this load was that there is a twin 9kW fryer available, so I wouldn't put it past him to go for that ??, cheers anyway?