Advice on 3Phase Hob

[smokeyc]

Hi there

I have not done a huge amount of work on 3phase.

I am installing a Induction Hob as part of a new Kitchen refurb- to be specific the hob is NEFF T59FSRX2.
It is a 11,100W with the ability to power limit and support single or three phase connection.

NEFF have not provided great support, so I've made an assumption that the power is distributed evenly amongst the phases.
I think it draws roughly 15A per phase, 19A when you add margin into it.
Forgive ignorance as I say the manuals are not overly informative for electrical demand or even how it selects between single and three phase.

The install I am doing will be in separate conduits surrounded by 50mm -100mm rockwool. (50mm wall, 100mm ceilings) for a 25m run.

So I have chosen 10mm singles and a protective device rating of 20A.

Does this sound correct?

 

[smokeyc]

Hi All
Thanks for the input, and I cannot believe it was there staring at me in the product information. I guess sometimes you cant see the wood through the trees. I feel like I have a good strong answer and now know with certainty and confidence. I do agree I think you can over think it; and I probably have. Though I am going to say putting those details in the manual, or assembly instructions would be much smarter. Thank you all

Hope this posts will be of some use to others working with 3 phase supplies.

 

[DefyG]

Though I am going to say putting those details in the manual, or assembly instructions would be much smarter.

Agreed but when some are clearly 'Badly' translated into English confusion results! which may have been the case albeit in part here.

 

[davesparks]

Hi Dave

As stated this is my first 3phase induction install.
Your comments seem a bit unkind and unfair, I am after all asking for help and advice.

I can't see that I've said anything unkind or unfair, for the most part I have just asked questions.

I made the assumption that you are an electrician and understand AC theory, 3 phase, cable calculations etc.

You mentioned breaker sizes for single phase and asked about 0.8; 0.8 is a worst case Power Factor used in a 3phase current calculation assumed for the induction electromagnets - used to calculate the current; equivalent to Ib (emphasis again I think and reiterate I am asking for help).

0.8 is not the worst case power factor, power factor could be far worse than that.
Power factor applies to both single or three phase.

So the SF comes from a number of things I have seen online for overload conditions

Are you sure you aren't looking at advice being given for installations in the USA? They do have some odd rules about percentages for safety factors and oversizing breakers.

In the UK we don't that sort of nonsense, certainly not for a simple appliance supply anyway.

Why don't you show me how you would do a NEFF 11kW 3phase hob installation with insulation, and what you would select and do?

Without knowing the full details of the job I can only hazard a guess, but I would expect a 20A supply in 4mm to be adequate. As far as the actual installation goes I would be doing my level best to install the conduit in such a way that it doesn't end up buried in insulation.

I know assumptions can often lead to problems but fact that this is being installed in conduit suggests that this is a commercial installation so I assume there will be voids bigger than the depth of the insualtion you could put the conduit in.

 

[Rockingit]

Property has 3 phase supply.

Doesn't mean it has to be installed as a 3ph device! How many 3ph ring mains and lighting radials do we normally install?.......

 

[brianmoooore]

Doesn't mean it has to be installed as a 3ph device! How many 3ph ring mains and lighting radials do we normally install?.......

It would be a strange decision to install it as single phase if a 3 phase supply is present. TP 20A MCB, 4mm2 supply, and 2.5mm2 HO7RN-F for the final connection.
Everything well within rating, running nice and cool, and the hob can be used flat out if desired.

 

[nicebutdim]

Doesn't mean it has to be installed as a 3ph device! How many 3ph ring mains and lighting radials do we normally install?.......

It does not, but OP had expressed a preference for 3ph installation.

 

[freddo]

Indeed, 3 phase is always a good choice for heavy loads, It's good many new houses are being provided with 3 phase as standard now. I'd love a 3 phase supply in my house.

 

[Lucien Nunes]

0.8 is a worst case Power Factor used in a 3phase current calculation assumed for the induction electromagnets

An induction hob works at high frequency and from the point of view of the electrical supply, looks like a high-power switched-mode PSU, rather than inductive coils themselves which are on the other side of the inverter circuit. How good the input power factor is depends on the quality of engineering design in the electronics.

Even where the supply is adequate to take the full load on one phase, there is an advantage to having it spread over three which is that the smaller each indivisible load current is as a fraction of the total, the more effectively diversity smooths out the bumps. It's better to have a bit of cooker and a bit of heater on each phase, than all the cooker on one and all the heater on another even if the maximum currents are theoretically equal. This is in addition to the theoretically-desirable-but-not-usually-very-important aspect of balancing the load for VD reasons.

Otherwise many thanks, I don't think this forum is for me.

I wouldn't give up on the place as there's no end of useful advice, however forum posts can be difficult to discern intent from and some text can appear quite blunt when no offence is meant.

Agreed, hang around @smokeyc, there are a lot of friendly, helpful, knowledgable people here. Replies sometimes come over as a bit brusque but some of the more prolific contributors plough through dozens of enquiries in a day and can't afford time to pussyfoot around. We need to grill the OPs to discover exactly what's what and weed out the numpties!