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Post by fish on Jan 18, 2024 20:56:17 GMT 12
I'll preface this post to say I will have to get a sparky in tomorrow. No offence guys, but I can't really rely on interweb advice for real life situations ;-) Tonight a light fitting decided to spit flames out the back, scorch the wall and make a shit tonne of smoke. Only it didn't trip the fuse. My question is why didn't it trip the fuse? - I would have liked it to, and I'd like to know my switchboard will stop the house going up in flames... It is currently giving me less confidence than a Labour led government. Background - light fitting is in the bathroom. House is 1969 and a number of fixtures and fittings are original, including this light fitting. I was in the shower. Damn thing sounded like a ray-gun going off. Lots of flashing / flames and noise. It seemed to go on for a long time. Probably in reality 2 or 3 seconds. The kids thought 5 to 10 seconds. It wasn't just a bang and done, this was a 'crack, bang, bang crackle, ack-ack-ack' kind of thing. Incidentally, once I saw the fire was out, I turned the shower back on to rinse the soap off - can't deal with emergencies naked and all lathered up y'know. Switchboard has a mixture of RCD's, MCB's and the old ceramic fuse with wire in it. This lighting circuit is on a Vynco LP 10 MCB (miniture circuit breaker, made in Chch by the looks). It has C10 marked on it, so I am assuming that is a 'C-curve' breaker - more on this soon. I've removed the light from the wall and made it safe for us to sleep tonight. It appears a wire at the back of the fitting has arc-ed and caused all the fun. I can see it burnt to nothing. The lightbulb itself appears to be fine, I suspect I can put it in another fitting and it will still go (might try that actually). Why would the circuit break not trip? Reading up on them, they protect from overload and short circuit. But not leaky earth, you need an RCD for that. It is a 10 amp unit, and it should respond within 10 milliseconds (0.1 of a second) BUT it needs to meet the criteria of short circuit current first. For a B-curve unit that is 3-5 times full load current, so 30 to 50 amps. If it's a C-curve unit that is 5 to 10 times full load current, so 50 to 100 amps. Is it possible the light fitting could throw flames out the back for 2 or 3 seconds and not trigger the short circuit current? It doesn't sound plausible to me. Even for a C curve - noting that B-curves are recommended for residential situations, especially things like lighting circuits where you don't have anything with a start up current on it. Is it possible the MCB is faulty? Is it possible I'm up for a shit-tonne of spending and multiple sparky invoices? Couple of references below www.vynco.co.nz/products/circuit-protection/dms-breakerswww.consumerunitworld.co.uk/what-is-an-mcb-and-how-does-it-work-328-c.asp |
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Post by fish on Jan 18, 2024 21:07:36 GMT 12
Couple of pics for context  I see the thing has loaded sideways. Gutted about the wall paper, that is original and impossible to replace. Been in the house 13 years and been desperately trying to avoid refurbishing the bathroom - sooo much opportunity for scope creep... I'm hoping some jiff will get the scorch marks off and I can kick the 'renovate the bathroom' can down the road another decade.  witchboard with Circuit breaker in question in the middle, orange switch. |
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Post by eri on Jan 19, 2024 5:29:50 GMT 12
presumably the arcing was low current
old houses with old wiring are a bit of a lottery
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Post by em on Jan 19, 2024 6:51:34 GMT 12
That could be an insurance issue if it’s not up to standard . See if you can find an understanding sparky like I did and re-run all the wiring yourself and get them to do all the connections and sign it off . It’s not expensive , I went to the electrical wholesaler for bulk rolls of wire and the young fellow at the counter quietly told me to go to Bunnings “it’s way cheaper “ he said . From memory it was $150 for 100m of lighting cable and a bit more for heavier duty for the power powerpoints , that was pre Covid so it will be more now .
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Post by Fogg on Jan 19, 2024 8:44:10 GMT 12
Jeez! 😳
How old is the house (presume wiring is original)?
Sounds like you and the whole family dodged a bullet there - could have been so much worse…
I know you want to tackle the root cause but meanwhile, presume your smoke alarms are all tip-top?
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Post by fish on Jan 19, 2024 9:03:07 GMT 12
Jeez! 😳 How old is the house (presume wiring is original)? Sounds like you and the whole family dodged a bullet there - could have been so much worse… I know you want to tackle the root cause but meanwhile, presume your smoke alarms are all tip-top? Fucking smoke alarms! I've had 3 different alarms give false alarms in the boys room. Twice at about 1 am of course. We had the same brand on the boat and that gave us a false alarm at, you guessed it, 1 am during our summer cruise. It is either insects or humidity. The specs say they can handle humidity up to 95% - not sure what we are supposed to do in Auckland when it is nudging 100%. I've changed brand, so far, so good. I've got 5 alarms across the house, in every room accept for the laundry and bathroom, where this happened. Short story is yes, I'm a bit anal about smoke alarms. Also have 3 fire extinguishers and a fire blanket in the house. Which reminds me, I need to go and refresh my knowledge of their locations. House is 1969. The wiring is in good order, it is the modern style PVC sheathed, not the dodgy 1930's style rubber sheathed that degrades and falls off. It is a timber floor on piles so I can inspect all the cable runs under the house. The switch board however is a real mixed bag... |
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Post by DuckMaster on Jan 19, 2024 9:06:46 GMT 12
Couple of pics for context View AttachmentI see the thing has loaded sideways. Gutted about the wall paper, that is original and impossible to replace. Been in the house 13 years and been desperately trying to avoid refurbishing the bathroom - sooo much opportunity for scope creep... I'm hoping some jiff will get the scorch marks off and I can kick the 'renovate the bathroom' can down the road another decade. View Attachmentwitchboard with Circuit breaker in question in the middle, orange switch. That panel is as old as. So old they have aspestos in them. You had a near miss! Time for a new panel with new breakers and new wiring. Those old houses often have no earth on the light circuits. You need RCBO's installed on all the house circuits. Even the range gets one. Only the hot water doesn't get one these days. |
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Post by fish on Jan 19, 2024 9:20:22 GMT 12
That could be an insurance issue if it’s not up to standard . See if you can find an understanding sparky like I did and re-run all the wiring yourself and get them to do all the connections and sign it off . It’s not expensive , I went to the electrical wholesaler for bulk rolls of wire and the young fellow at the counter quietly told me to go to Bunnings “it’s way cheaper “ he said . From memory it was $150 for 100m of lighting cable and a bit more for heavier duty for the power powerpoints , that was pre Covid so it will be more now . I didn't really want you to mention the 'insurance' word... I've no concerns about the wiring itself. In fact it is probably the best part. House is timber floor on piles, so I can inspect all of the cable runs easy. About half the house and wiring is newer than the other half, but it is all modern PVC sheathed cable, not the old 1930's style rubber sheathing that falls off and starts fires - I would think that would be an insurance issue, and my understanding is houses of that age get pulled up at re-insurance time and need upgrading. I know my father's rental did. In this instance I would think it was a one of failure, not a known problem, and that is exactly what insurance is for. The switchboard is a real mixed bag. Still has ceramic fuses on it. But this circuit isn't on one, and it still didn't blow. I've had a quote previously for replacing the whole switchboard. I thought the quote was $3k, but the missus recons it was only $1.5k, I'm sure I would have just done it for $1.5k. Thinking I'll do it regardless now. We have had a light switch fail, as in burn out. We looked at getting all of the light switches renewed with matching modern ones, but the cost was a bit next level. I think it was $150 per switch or something. We have an extraordinary number of light switches for the size house. The total job of doing the switchboard and light switches was some impressive scope creep. Missus was one step off a full reno so the wall paper matched the new switches, or I think the new switches didn't exactly cover the existing holes in some cases and it just grew arms and legs. My current plan is to replace all the original light fittings. Most in the house have already been renewed. There are two others in the laundry area of that same type, and 3 in the master bedroom that are original but a different type. Oh, and one over the dinning table I can't find bulbs for anymore - was hunting through Bunnings for the old incandescent bulb for that yesterday. Basic light bulbs seem to have gone the way of affordable eggs - some lefty-poof-tree-hugging-vegetarian has decided they know better and wont let me buy what I want to choose... What I'm really wanting to understand is why the fuse didn't trip, and if changing to RCD's would have tripped it? Noting that the earth leakage is different to a short circuit current, but that RCD's are generally far more sensitive. |
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Post by em on Jan 19, 2024 9:26:28 GMT 12
Had near miss fire situation on the boat recently and asked my electrical engineer mate why it didn’t trip the breaker (freezer cabling melted) . It didn’t make any sense to me but he said something about loose connections and resistance causing heat but no current spike to trip the breaker . Could well be the light fitting had a loose terminal screw or something ?
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Post by fish on Jan 19, 2024 9:31:58 GMT 12
On the insurance question, who thinks I should report this to the insurance co?
I don't want to make a claim, I'm fairly sure the cost of repair is less than our excess, it's more about the full disclosure rules.
That said, if we can't get the scorch mark off, it may require re-decorating, which could go over our excess...
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Post by DuckMaster on Jan 19, 2024 11:01:11 GMT 12
What I'm really wanting to understand is why the fuse didn't trip, and if changing to RCD's would have tripped it? Noting that the earth leakage is different to a short circuit current, but that RCD's are generally far more sensitive. RCD's only will trip if there's a 30ma differential across the phase and neutral. That means electricity has to be escaping via another path to earth. Your neutral and earth are joined at the switchboard and at the power line in NZ. It's called the MEN system. RCDs stop electrocution. They don't stop short circuits. We use RCBO's in NZ these provide the functionality of a RCD and MCB/MCCB in one. An RCBO will not work on its own unless your light circuit had a earth to provide a return path. Many old light installations like the one you posted do not have a earth. So if there's no earth then you would have to create one manually ie, by touching the light and touching something else that is earthed to create the path. Tldr; you're entire house should have a couple of RCBOs on it. It's money well spent and saves lives. An electrician can install these into your feed from the street very easily. As for the sparks spitting out the back, if there was no short to earth and the current didn't exceed the MCB rating then the sparks will continue until one of those conditions is met. |
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Post by fish on Jan 19, 2024 12:26:56 GMT 12
Reported it to the insurance co, just thought it's better not to muck around with those guys, and it was easy, just a phone call.
Expecting our sparky this afternoon to investigate.
DM, the light in question has an earth wire. Most of our light fittings are metal, I understand it is a basic code / legal requirement to have the metal casing earthed, which this one was. It is also fairly logical to earth a metal light fitting, so it doesn't conduct to you so easily.
We've got a couple of RCBO's on the switchboard. The house is a bit of grandpa's axe and where we have had work done have put in the appropriate gear. Looking at the photo it appears the RCBO's are on the kitchen from when I upgraded that, and possibly a circuit under the house that runs my water pump and EV charger.
As for asbestos on the switch board, the whole house is made of asbestos. 1/4 fibrelite with a stone veneer cladding. Tough as nails, and strangely the house doesn't leak like a modern one. I'm aware of the risks of asbestos, but I'm also aware of how to keep it in good condition / manage it. The only thing I have been caught out on is lead paint on the eves, lesson learnt on that one.
From what I understand, if the MCB wasn't triggered on short circuit then the RCBO wouldn't have been either. The mechanism for short circuit being excessive current. The RCD element of an RCBO being imbalance in the phases (via earth?). It is possible the shorting produced an imbalance, but am I correct in that if it's not via the earth it doesn't trigger it?
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Post by DuckMaster on Jan 19, 2024 13:10:51 GMT 12
Reported it to the insurance co, just thought it's better not to muck around with those guys, and it was easy, just a phone call. Expecting our sparky this afternoon to investigate. DM, the light in question has an earth wire. Most of our light fittings are metal, I understand it is a basic code / legal requirement to have the metal casing earthed, which this one was. It is also fairly logical to earth a metal light fitting, so it doesn't conduct to you so easily. We've got a couple of RCBO's on the switchboard. The house is a bit of grandpa's axe and where we have had work done have put in the appropriate gear. Looking at the photo it appears the RCBO's are on the kitchen from when I upgraded that, and possibly a circuit under the house that runs my water pump and EV charger. As for asbestos on the switch board, the whole house is made of asbestos. 1/4 fibrelite with a stone veneer cladding. Tough as nails, and strangely the house doesn't leak like a modern one. I'm aware of the risks of asbestos, but I'm also aware of how to keep it in good condition / manage it. The only thing I have been caught out on is lead paint on the eves, lesson learnt on that one. From what I understand, if the MCB wasn't triggered on short circuit then the RCBO wouldn't have been either. The mechanism for short circuit being excessive current. The RCD element of an RCBO being imbalance in the phases (via earth?). It is possible the shorting produced an imbalance, but am I correct in that if it's not via the earth it doesn't trigger it? If the short was to the ground wire, ie the metal light fitting, And the current was over 30ma then the rcd part of the RCB0 would of tripped the breaker off. The new electrical code requires that any additions have RCD installed in the circuit. This doesn't have to be on the switch board it can be on the outlet itself. Eg, those sockets you see in the bathroom with the test button. They are an rcd and meet the new code. As you get more and more changes done there comes a point when if is more cost effective to protect the whole house rather than the individual circuits. On my place I have two 40amp RCB0's. Every circuit in the house then hangs off one of those two, with their own MCB. (Except the hot water that's out on its own as its independent). It's not about a short to earth, it's about another return path via the ground wire. If the circuit is completed via a path which causes a imbalance at the RCBO which is over 30ma then it will trip. Yes that path could be via you, to the ground, and then back to the switch board. But it could also be via the metal device itself. So remember I said above that the ground and neutral are bonded at the switchboard. This is done before the RCB0. So if one of the phase or neutral wires in your light fitting made contact with the metal, which was connected to the ground wire, then assuming a clean connection, 50% of the current would be on the earth wire, 50% on the one that connected to it and 100% on the third wire. (using 100% for each side of the loop) As the earth wire is now current carrying all the way back to the power supply on the street, the RCBO sees this imbalance and trips. So assuming that a wire in your light fitting came into contact with the light chassis, and started sparking, then yes the RCB0 would of tripped. But if the phase and neutral only came into contact with each other, there would be no imbalance and they would spark until there was enough current to trip the MCB which may or may not have ever happened. |
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