So, the two chip fryers for our new burger joint each have 2 x 6 kW heaters in them, so a grand total of 24 kW. The electrician who is doing the work (and whom I don't totally trust) is proposing feeding 4 x 6 kW feeds from the board, to 4 isolation switches. This split across two phases. Sounds reasonable so far ?? But, he's telling me that the RCD breakers to go in the board, that he needs to feed these 4 lines, are about fifty quid apiece. That seems a lot to me. What sort of breakers should these be ? Bog standard single pole 32 amp ones ? Or am I missing something here ? I'm no expert in electrical work, but I don't want to get charged for something that I don't need. The board is brand new, just installed by the landlord's own contractors. The electrician agrees that it is a "top quality unit that complies with all the latest regs" - his words.
Now that I don't know, Andy. Is there something that says it needs to be these combo types, or is it just his opinion or what ? What is actually required to comply with any regulations, and be 'sensibly' safe ? Initially, he assumed that the total load on the fryers was 12 kW, and came back with a quote for all the electrical work, which I thought was a bit steep, but we needed it getting on with, and a friend had recommended him, so we said ok. When we realised that he had specced it wrong, we told him, and he initially said that *we* must have it wrong as that was far too much of a power requirement. We assured him that it was right, and pointed him at the website for the fryers, which said so. He then upped the quote by 300 quid and said that this was because of the additional load now required. When I queried the cost of this, he blustered and bumbled and said it was because the breakers required were very expensive and he'd now got to put in two more feeds and isolators. The run is about 6 metres back to a brand new panel on a brand new three phase supply. The fryers are nothing more than a sophisticated commercial version of the 3 kW deep fat fryers that we all have sitting in our kitchens at home.
Well, I assume you'll have to (or want to) use RCD protection somewhere, depends if you want overall protection (where if one item causes a leakage trip, they will all be shut down) or individual protection (so that only the faulty item is isolated)
Within a commercial kitchen, I'd have no idea.
One overall RCD and individual MCBs would be equally safe, but I assume the reason for having two separate fryers is a certain degree of independence, so would tend towards the RCBO route, though it will be the most expensive.
No need for RCDs of any kind, provided all the following apply:
- TN-S or TN-C-S supply;
- all surface-wired (SWA, hi-tuf, conduit/trunking);
- nothing to the contrary in the appliance manufacturer's instructions;
- earth fault loop impedances (Zs) all within the usual limits;
- no socket-outlets on these circuits.
If you want belt and braces safety I'd go for supplementary bonding across all the exposed metalwork in the working area - cheap and effective. Make sure the Zs tests are done before connecting the bonding though, otherwise a bad earth could be masked.
OK. Understood. Presumably, the main breaker / input switch on the panel performs the RCD function ? Four baskets of chip frying capacity are needed at busy times. Frozen chips rapidly drop the temperature of the oil, which then has a recovery time of a couple of minutes, depending on how powerful the heaters are. The 6 kW ones in the J12's are by no means the biggest you can get. In takeaways, you will often see chips get moved from one fryer to another during their cooking. This is to 'finish them off' in a fryer that's at full temperature. It stops the chips being soggy. As to the situation if one fryer became faulty in an RCD trip way. As we are intending having each fryer circuit on its own isolator switch, I guess the faulty one could effectively be 'taken off the board' by switching its feed off, allowing the other three (or two possibly, depending on the nature of the fault), to carry on working. Alternatively, if it is configured as four separate 6kW feeds, each on its own breaker at the panel, the breaker for the appropriate faulty circuit could just be flipped out, if the nature of the fault was not just taking that breaker out on its own ?
Thanks for all the valuable input. I just like to understand these things, and know that I'm not being taken for a mug. You wouldn't believe some of the 'rogue traders' we've seen already, and although this electrician was recommended to us by a friend, neither I nor the missus and daughter really 'took' to him from the start, and there's been a few little bits and pieces in our dealings with him so far, that have done nothing to improve that feeling. I'm sure you know how it is when you get this sort of feeling about someone.
Well it could, or you might not have any, but as I say, I don't claim to know if there are any specific requirements in a commercial setup, if Mr Wade says RCD protection isn't mandatory for you, I'd tend to listen.
To know if your sparky is taking you for a ride you need to know what type of breakers he is proposing and why, also what other protection already exists on the installation. Not ideal if you don't entirely trust who's working for you ...
You may be able to cope with two isolators - and basically a fryer on each rather than a side of a fryer on each.
Since he is talking about feeding each fryer from two phases, he may be proposing to use a 3P+N breaker rather than a pair of single phase ones. Needless to say these breakers are more expensive.
(e.g. a Hager single phase MCB from TLC is three quid plus VAT, the 3P version is ten times the price! The 3P MCBs also have a 10kA breaking capacity while the single phase ones only 6kA normally. Higher capacity may be required)
Looking at the spec here:
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seems to suggest you can either feed each fryer with two 26A single phase feeds, or with two three phase feeds, in which case it draws power from only two of the three phases, and takes 13A per phase.
(assuming the distribution of loads on the CU permits it, I would probably opt for feeding fryer 1 left and right from two single phase breakers on one phase, and the other fryer from two single phase breakers on another phase.
Depending on how he does the wiring, you may not need RCD protection for them anyway.
Could you do us a photo of the CU?
Most of the commercial ones will take a mixture of breaker types including single phase and three phase.
Thanks. Good to have chapter and verse. Today, the electrician should have been back, but he hasn't turned up, so that's him blown out of the water anyway. At the moment, the extraction installation people are there finishing up making their connections to the fused spurs which this guy had put in ready for them. The daughter has just rung me to say that one of these guys has just shown her that the neutral and earth were connected backwards in one of these spurs. Even for this guy, I find that hard to believe, but when he came the first evening, having already let us down during the day because his "van had broken down", he did have another guy in tow to help him, and I took to him still less ...
A guy that I do work for and trust implicitly, has just told me that his stepson is a fully certified electrician, so I think I will get him in to finish up, and check the rest of what's been done so far.
As to the installation, it is brand new. A new three phase supply and a new board, put in by the landlords own contractors. The building was originally
2k sq ft, and the supply came into the left side of the building. The building has now been divided into 2 x 1k sq ft, and we have taken the right hand side unit. All of the existing electrics for our side of the building were disconnected from the original board, and a new board was installed at our side, and the original electrics reconnected to this. A new supply was put in by NG or EON or whoever it is does the work on the supply grunt side these days, and then a new three phase meter was fitted yesterday. All proposed new wiring will be surface, and the circuits for the fryers will be completely independent of any socket rings.
Given that we need to feed these two 12 kW fryers, which each have two 6 kW heaters in them to make up that 12 kW, and that the manufacturers say that they can be connected single or dual phase, what would you consider to be the most versatile - from an isolation point of view - cost effective, and load-sharing way of providing the necessary power ? Four 6 kW feeds split across two phases as the original electrician was going to do, or some other scheme ?
Assuming these are the major loads and everything else is fairly small stuff I'd be inclined to run them in 2-phase configuration, using a different combination of two phases, e.g.
- Fryer 1: L1+L2+N
- Fryer 2: L1+L3+N
then split the lighting and small power as evenly as you can across L2 and L3. Anything with a 3-ph motor in it will of course need all three phases, and possibly N.
If each fryer is split across two phases then use the three phases for load balancing. If you want each one completely independent, supply each one from a single phase, but a different phase to the other. That is what I would do with that load unless there are other compelling reasons.
If each would happily run on 6KW, then use all three phases. if they /need/
12Kw, then each on a single phase.
Three phase RCDs are available but as others have said (with provisos that you seem to comply with) you don't absolutely need them. If each fryer was on a single phase then single phase RCDs (which are cheaper) could be used.
Hmmm. I don't understand enough about three phase to fully understand that. I'm not really following the bit about them 'needing' 12 kW. If that is what they are rated at, isn't that what they 'need' ? There are four independent elements to feed - two in each fryer, one per tank. Each element is rated at
6 kW. I'm sure the electrician that we've got now will understand it all. I'm meeting with him in the morning, so I'll see what he thinks is the best feeding scheme, based on what he sees when he looks at the job.
You can basically choose to feed each element from one phase or two. If you do it on one phase it will suck 26A on that phase. If you do it across two it will draw 13A from each phase. There are pros and cons, but in the end it will probably come down to which can be done with the cheapest protective devices, and which best spreads the load over your three phases. Given you have four loads and three phases, you are not going to get a perfect distribution in this circumstance since each tank can only use two phases at a time and not three.
One possible 3 phase allocation:
Tank Phases
T1 L1 L2 T2 L1 L3 T3 L2 L3 T4 L2 L3
Would give loads of 2 x 13A on L1, 3 x 13A on L2, and 3 x 13A on L3. You would then probably want two three phase MCBs (£70 ish) - one per fryer.
Alternatively, using single phase:
Tank Phase
T1 L1 T2 L2 T3 L3 T4 L1
2 x 26A on L1, and 26A on each of the others. Four single phase MCBs (£15 ish) - allowing isolation of half a fryer.
Or:
T1 L1 T2 L1 T3 L2 T4 L2
2 x 26A on both L1 and L2, nothing on L3. Using two 63A MCBs (£8 - £30 ish) if available for your CU.
Thanks John. All clear now. The new electrician turned up this morning to cost and spec the job. I gave him a copy of the specs for the fryers, and he took a lot of notes about the board and what else we needed. He has already come back with a (very reasonable) price to sort out the three switched spurs for the extraction equipment that the first guy had already made a start on putting in, and his guy is there right now doing this. We are expecting the quote for the rest of the work, which has a looser time constraint on it, in the next couple of days. It will be interesting to see what feeding scheme he comes up with for the fryers, based on what he saw this morning, but unlike the other guy, I have total trust that whatever he says, it will be appropriate for the circumstances, and realistically priced.
Not least because me and his stepdad are good friends and business associates, and that he went to school with my daughter !
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