Pop Quiz - Trainees Cooker Question

[Nigel]

So I am going to ponder a design question as a potential real-life situation for you all to consider.

Rules:

• The winner may not necessarily be just a correct answer. Backing up you thoughts with detail and Reg numbers will get you above your competition.
• TRUSTED ADVISORS will decide the WINNER. Likes are encouraged but the answer with the most 'WINNER' votes will be the winner. Trusted Advisors can vote more than once but TRAINEES cannot use the WINNER button.
• Bouncing ideas off of one another is encouraged as is probing questions from Trusted Advisors.
• Winner will be decided Sunday night. The prize is this. Prize will be made available to pick up from your local Rexel branch.

Question:

A customer wants to change their gas oven and hob standalone unit to an all electric one. The oven they are installing is an Electrolux EKC6461AOW Ceramic Electric Cooker.

You attend the house and survey the run. The CU is a BS3036 type. The installation will be chased into the wall which is all brick and the floor boards are able to be lifted to wire through the ceilings. There is really old insulation in the ceiling and is about 50mm in depth. The circuit will be a 25 meter run. Bonding to the gas and water is 2.5mm.

The customer has asked to not have an isolator installed and wants the circuit connected directly to the CU. If she absolutely has to have one she wants one with a socket on. She wants your advice on if she has to have an isolator backed up by a Regulation, if possible.

The customer would like to understand fully how you are going to do this job and wants to know how what size cable is being installed and what type of cable. The customer also wants to know if there are any other issues that you can see with the existing installation that may need to be addressed and the reason.

There are no silly answers or ideas. All ideas are welcome in this section of the forum so do not be afraid to give it a shot with your best answer.

Good luck and enjoy.

 

[MDJ]

Too difficult to try to answer , a good puzzle for the trainees definately.

 

[gazdkw82]

Earthing arrangement?
Size of the tails?

 

[Nigel]

Earthing arrangement?
Size of the tails?

25mm tails.

TN-C-S (PME)

 

[littlespark]

Does the customer make a good cup of tea and does her husband work away a lot?

 

[Resu]

Sounds like a nightmare customer! Good luck guys!

 

[gazdkw82]

Right, I've had a go. Best I could do with the kids screaming around me (the other half is working late)

I know I've made mistakes but it's been over a year since I touched any design scenarios.

Best I could do for now

 

[MFS Electrical]

Liking the regs @gazdkw82

 

[Nigel]

Right, I've had a go. Best I could do with the kids screaming around me (the other half is working late)

I know I've made mistakes but it's been over a year since I touched any design scenarios.

Best I could do for now

View attachment 44784

View attachment 44785

Excellent start.

 

[telectrix]

so my idea of a few yards of red/black 7/029 salvaged from a recent rewire and piggy backed off the ring with a nail in the 30A 3036 is a non-starter?.

 

[Jay 1987]

firstly i want to say i hope the staff will give a full explanation of this because i am absolutely baffled hahaha

anyway shouts out to gasdkw82 nice work mate

my contribution is more research based then working out figures.

its not much and it maybe wrong

however here we go......

firstly we rock up to the house and id let gaz do the maths and dimensions and this would be my bit hahaha

regarding circuit protection


BS 3036 semi-enclosed fuses cannot be relied upon to operate within 4 hours at 1.45 times the nominal current of the fuse element.

not exactly sure what this means...... however

Correct protection can be obtained by modifying the normal condition In≤ Iz such that the fuse rating does not exceed 1.45/2 = 0.725 times the rating of the circuit conductor. For this reason, larger cables may need to be selected where overload protection is provided by semi-enclosed fuses than when it is provided by a cartridge fuse or fuses or circuit-breaker (Appendix 4 of BS 7671 and Guidance Note 6 give further guidance).

So this has a bearing on the type of cable and size used its in relation to circuit protection. (i think)

If she does not want a isolator but wants it connected to the consumer unit then firstly not sure if thats legal or not however what i found was according to reg 533 01-04 it requires fuse elements in semi enclosed fuses to be in accordance with manufacturer instructions. where this is missing table 53 a of bs 7671 gives some guidelines and for the cooker she is having which is 240v, the nesscessary fuse is 30A and the the fuse element required for a 30 A fuse is 0.85 mm of tinned copper wire.


this is all i managed to source . can't wait for the real explanation lol

 

[Nigel]

So I havr not forgotton but I have been really busy.

We are seriously lacking answers here and have yet to declare a winner.

So another few weeks will be added.

 

[Jay 1987]

Can we have a small clue or guidance as to what we are supposed to be looking for ?

 

[Richard Burns]

Can we have a small clue or guidance as to what we are supposed to be looking for ?

You want to define the size and type of cable required to safely connect the oven to the CU. Taking into account the description of the cable run, installation methods, protection type and connected load.

You want to identify any other issues that may need to be addressed. Refer to the description of the installation and identify any problems.

You need to assess if a local isolator switch is required and if so why.
Reference the regulations on isolation and switching.

From your post you have stated that rewireable fuses take more current (than 1.45*In as is used for MCBs) to ensure disconnection on overload so the cable will need to be bigger to not overheat before the fuse goes. This is a good start on defining the cable size.
gazdkw82 has made significant inroads into the
calculation and information that show the approach expected.

Keep on thinking about it and checking the regulations for the items mentioned in the description.

 

[Jay 1987]

You want to define the size and type of cable required to safely connect the oven to the CU. Taking into account the description of the cable run, installation methods, protection type and connected load.

You want to identify any other issues that may need to be addressed. Refer to the description of the installation and identify any problems.

You need to assess if a local isolator switch is required and if so why.
Reference the regulations on isolation and switching.

From your post you have stated that rewireable fuses take more current (than 1.45*In as is used for MCBs) to ensure disconnection on overload so the cable will need to be bigger to not overheat before the fuse goes. This is a good start on defining the cable size.
gazdkw82 has made significant inroads into the
calculation and information that show the approach expected.

Keep on thinking about it and checking the regulations for the items mentioned in the description.

Ok thanks