Advice sought (long read - apologies)

Discussion in 'Electricians' Talk' started by FifeGolf, Jan 18, 2021.

  1. FifeGolf

    FifeGolf New Member

    Hi all,

    I am new here seeking advice on whether there is a quick fix (or something obvious I missed) or if I need to get a spark (easier said than done just now).

    This is a long read, so I apologise in advance, but looking over the forum most of the time detail is asked for, so I will give as much as I can.

    At the start of lockdown we bought a new house, due to Covid etc the timeline pushed out and pushed out and finally we moved in at the start of December.
    One of the attractions of the house was a detached garage with power as I have a hobbyist woodwork shop type set up to go in there.

    So last week I finally got round to unpacking and installing my machinery in the garage. Static machines are;
    1600W Mitre Saw (x2) - one hard start, one soft start
    2100W Table Saw - soft start
    2200W Planer/Jointer
    1600W Router Table
    950W Pillar Drill (Induction Motor)
    650W Band Saw (Induction Motor)

    Each machine is accompanied by a shop vac at 1800W.

    In addition there is a small 30W hifi that runs for backgorund music. Now obviously all of the machines only run one at a time (save for the shop vac which starts up with each machine via a "take off" socket where the wattage allows).

    Now to the problem, I started making a new outfeed table for the table saw and using the hard start mitre saw I noticed that the lights were dimming very briefly on start-up. Never thought much of it, later I got cold do I plugged in a 2KW fan heater and went about making the table.

    After about 15 minutes the power went off. So I checked the CU in the garage and it was fine. So went in to the house and found the main CU has a "Garage" MCB (32A) which had tripped.

    After re-setting, this happened twice again. Each time, it was just random timing. (not like a machine started and it tripped).

    So I did a bit of investigating of the system. And I found the following;

    The main CU 32A MCB feeds the garage on what appears to be 4mm SWA (it's diameter is 16mm which seems to tally with 4mm).
    This SWA is terminated via a gland at a metal garage CU (The earth on the gland "banjo" is to the earth rail via what looks like a M5 galvanised bolt) which houses 2 x 32A and 1 x 6A MCB from a 40A 30mA incoming RCD - (I think that's the right terminology).

    There are two 6ft LED batten lamps running from a 2 gang metal switch at the door and 2 security lights that seem to be hard wired "always on" to the 6A MCB along with the feed to the light switch (so 2 browns coming from the 6A MCB).

    Each of the 32A MCB seem to support a ring circuit of sockets on 2.5 T&E, but its' a bit weird. One set of sockets (4 x double and one single) are metal clad surface mounted and the others (8 x double) are recessed into the MDF clad walls using what appear to be plastic lining boxes.

    I took each socket off to check for loose connections but they all seem fine, each socket has one incoming and one outgoing cable which seems to start and finish at the MCB.

    Is there an obvious reason for this tripping at the main CU rather than the garage and it's random nature and I can fix this quickly and myself or is there something sinister at play and I need a spark?

    At the moment there seems to be a bit of a wait for trades people in my area (Fife, Scotland) due to Covid and them just seemingly busy.

    Very frustrated that I can't seem to use the garage properly after it being my big excitement of buying the house (don't tell the Mrs that!)

    Apologies for the long post but wanted to give as much detail as I could.
  2. FifeGolf

    FifeGolf New Member

    Forgot to add an important piece of info.

    The SWA run is approx 15m maximum. First 10m is under the floor of the house, I looked under a hatch and can see it's sitting on the ground, not clipped to anything. Of the last 5m, 3m of those if buried in the ground but I couldn't tell you how deep or even how long it's been there.
  3. FlyByNight

    FlyByNight Active Member

    15m of 4mm should support 7+kw or 34 A with just a small voltage drop.

    At worst you would be taking 1600 + 1800 + 2000 = 5400w which is less than the MCB.

    Do you have access to a current clamp meter? You could then see what you are pulling through the SWA.
  4. FifeGolf

    FifeGolf New Member

    Thanks for the reply.

    I don't have access to such a device. I think getting it checked would be best if it's not something obvious that could be wrong. I mean, on the surface, it "looks" like it's a nice a tidy job, well installed (except the oddness of the recessed sockets) but just annoying that on cold days the power will trip if I turn a heater on.

    7KW would be the total for the SWA? So wouldn't even help if I used the heater on the "other" ring? (I think I had everything plugged in on the recessed socket side).
  5. terrymac

    terrymac Screwfix Select

    Does MCB ever trip when heater is NOT in use ?
    BiancoTheGiraffe likes this.
  6. FlyByNight

    FlyByNight Active Member

    As it is the house MCB that feeds the garage and then the two rings - it would not make a difference.
  7. FifeGolf

    FifeGolf New Member

    I'll be honest Terry, I haven't really used it long enough to know if it does. It was really just Saturday when I was making the outfeed table and cutting timber, it was -2 degrees so popped the fan heater on and that's when it was happening. It has been ok for about an hour before the heater went on (except the lights dimming briefly).
  8. FifeGolf

    FifeGolf New Member

    If I need to call a spark out, would it be worth my while getting him to up the cable size and main MCB size? I mean, if I have to pay him anyway, might as well get it sorted sorted.
  9. terrymac

    terrymac Screwfix Select

    You would be well advised to get an electrician in to investigate ,could be the house MCB is a little oversensitive ,but with the loading you have a heavier supply would make sense long term anyway.
  10. FifeGolf

    FifeGolf New Member

    I suspected as much. If I am having to pay I might as well get it beefed up for longevity's sake.

  11. FifeGolf

    FifeGolf New Member

    Got a spark coming out to have a look on Wednesday but any work needing done could be April :eek:
  12. Mr Rusty

    Mr Rusty Screwfix Select

    First, I am not a sparks, but I am a woodworker and have had my share of blown fuses and breakers. (for example, I found you can cut 3 bricks in half with a 2600W soft start diamond saw with a 2kW fan heater plugged in to the same extension before the 13A fuse pops (and the plug melts a bit) whoops!) At the moment I have a very temporary supply with an extension cable slung across to my garage (sparks lined up to make the proper connection). I have one machine ( a 1500W thicknesser) which will take the fuse out if there is almost anything else plugged in to the extension, and yet my 1500W soft-start saws and 1100 vac live side by side quite happily - the thicknesser just seems to have a high start current.

    Conclusion is that it is almost certainly the inrush current, and I bet that's the same problem you are having - hard start electric motors can draw ~6X rated current for a short period when they start. The remedy may be a "C" rated breaker instead of a "B" rated - but as I say I am not a sparks, and you really do need one to make the right choice.
  13. FifeGolf

    FifeGolf New Member

    I get what you mean but it's definitely not the machine start-up that's doing it as it will just be random times even when nothing but the heater was running.
    Not really spent enough time out there to know if the heater is the root cause. But if I can get it beefed up to, say 10mm SWA then that can only help the situation.
  14. FlyByNight

    FlyByNight Active Member

    You need your electrician to decide what type of breaker is needed - as MrR mentions C-curve rather than a standard B for example. Get him to look at both indoor and garage CU, ensure there is suitable RCD/RCBO protection, breakers at right level and increase the cable - he may suggest 6 or 10 or even stay as is.
  15. sparky Si-Fi

    sparky Si-Fi Screwfix Select

    Sparks needs to look at this my flower and get a site visual is my best advice

    You can spend hours in this chat room and getting all sorts of advice, but what you need is a spark with you (well 2mts away anyway) we cant do this job from home!
  16. FifeGolf

    FifeGolf New Member

    Why is your flower needing a spark? What a strange fellow.

    Spark is coming out on Wednesday evening, he gave me a courtesy call earlier to get more info on the current situ/set up so he has a better idea when he gets here.

    Asked my usage and possible future use (which includes a 3kw cabinet saw if I am a good boy), so he is hinting at 10mm SWA and as above spoke to me about type C mcbs. I just said yes and no as required and see what he says Wednesday.

    Only issue is he won't be able to anything for a while due to workload.
    I might be able to live without a heater if thats where the problem lay until it's fixed.
  17. FifeGolf

    FifeGolf New Member

    So the Sparky has just been, earlier than expected but I'm WFH so no odds to me.

    His appraisal was a little less encouraging that I'd originally hoped.

    He found that one "ring" was not complete so was essentially just a radial of 8 double sockets on 2.5mm T&E to a 32A MCB, which he says isn't right and could have been dangerous. But that's an easy fix.

    The second ring to the surface metal sockets was fine, save for an earth fly lead missing in the last box.

    His recommendation after using a clamp meter and getting me to start the table saw and hard start mitre box was to have a type C MCB to take the momentary uplift in demand. Seems sensible advice as someone posted on here.

    The lights were all fine save for the SWA to the shed (lights only) the armour hadn't been earthed properly in a plastic box. Again he says that's an easy fix.

    The big issue seems to be the SWA from the house. I was planning on replacing anyway so the cost wasn't the shock, it was the state that it was in.

    Turned out to be a weird braiding armour rather than the steel wires and internally the cable is full of water and the braided metal is all corroded, he says it's a total earthing disaster waiting to happen. Also we pulled a but up and it was no more than 5cm under the grass and not a conduit in sight.

    He estimated the cable is 25-30 years old min.

    So he recommends 10mm SWA from the house which I need 13m of (so my 15m guess wasn't bad).

    I feel very, very glad that I got this checked before I start using quite heavy but also quite expensive machinery in the garage.

    All in all, I am looking at £300 of work (If I dig out the trench and run the conduit for him) but get the feeling that left unchecked could have ended up far more than that (especially if a £700 mitre saw gets damaged by any faults!)
    daviesm1976 and Mr Rusty like this.
  18. FlyByNight

    FlyByNight Active Member

    Good result, although will question need for conduit/duct for SWA unless he wants to pull though - you will have to dig, so the extra cost minimal and not worth arguing. £300 for a decent check over, some initial fixes and a final cable install - a reasonable price around my way.
  19. FifeGolf

    FifeGolf New Member

    Yeah, he reckons duct will add a bit of longevity as the ground around the side of the garage is a bit water retaining (hence what's happened to the old one I think). It won't take me long to dig as I need to lift a couple of slabs adjacent to it anyway.

    Not going to argue at £300 but he can't fit me in until 23rd Feb. So not too happy using the garage until then.
  20. FlyByNight

    FlyByNight Active Member

    Why not get the dig done, and tell him that you can be available at an hours notice (if you can) and if he has a spare couple of hours could come and do one or two of the smaller tasks as fill in? It might be "bitty" but he will fill spare time and you may have it finished earlier.

    At least teh digging will keep you warm!

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