Grumbles, Glory and All Your Off Topic Discussions

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robsmith
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Message 108473 - Posted: 15 Jun 2022, 19:17:02 UTC - in response to Message 108472.  

Then add high voltage and high power, plus a smattering of not-50Hz stuff and life gets even more exciting, or enlivening depending upon one's point of view and location when a fault arrives...
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Profile Dave
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Message 108475 - Posted: 15 Jun 2022, 20:12:26 UTC

My comms experience is up to 12KW going to antennae on HF. (Six years in signals.)
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Sirius B
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Message 108480 - Posted: 16 Jun 2022, 3:41:33 UTC

At times, it's amazing how conversations provide beneficial information.
Bumped into an old colleague & his wife while shopping yesterday. Got asked if I was retired yet.
Told him, officially yes but not yet in receipt of pension.
Gave me several sites to visit as, if like him, not entitled to any benefits, but may be entitled to some financial assistance.

Glory (I hope).
Winter fuel payment - looks like I'm entitled to it.
Also, there will be a £300 cost of living payment added to this years WFP.
That's going to be a nice Xmas this year. :-)
Grumble.
Several sites, all old age related say the same. The WFP is worth £100-£300. Each site provides a link to .gov.uk to ascertain what entitled to.
Government states £500, so e-mailed them a question. Awaiting answer.

Glory.
Check with local council & using their benefit calculator find (based on 2022/23 bill) that instead of having to pay £23.20 a week, will only have to pay £0.38 a week.
Shame it can't be pro-rata.
Wonder if I can claim 75% of this years bill back.
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Profile Gary Charpentier
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Message 108481 - Posted: 16 Jun 2022, 4:50:40 UTC

So many possibilities for a fire start. One of the most obvious is too much flex in a cable breaking conductors resulting in extra resistance and hence heat, which continues to degrade the metal conductors.
Possible for insulation to rub out creating an undesired circuit path and as it isn't a good connection it will generate heat even if it isn't at fault levels of current.
A "short" to some part of the building construction, which is not well earthed again resulting in heat but not enough current to trip a protector.

Some year ago a neighbor had a fire start inside a metal conduit from the weather head to the meter. Likely a wire found something to slice through the insulation some decades before when the house was built and it just took years to work its way to a problem.

As to fire brigades, on this side of the pond they just cut the distribution drops with an insulated cutter. Think like for cutting tree branches. Obviously they don't cut the high voltage side, just the distribution side. However with solar and power walls, they face other challenges to putting water on the flames today

YMMV
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robsmith
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Message 108486 - Posted: 16 Jun 2022, 7:32:26 UTC - in response to Message 108482.  

Well in the case of my neighbour, enough current flowed to really upset the transformer, so obviously well over the 100A he should have been getting. Why wasn't this fused at the transformer? No cable should ever have no protection.

Well this is just so wrong...
Transformers can make a surprising amount of noise when feeding an arc or a significantly out of balance load. Also they sound louder at the dead of night as there is far less other background noise to hide them.
Hmm, this shows how much you understand cable rating. If the domestic fuse was 100A the cable wouldn't rated to carry only 100A, but several times that, possibly up to several kA, but probably around 1000A in fault conditions.
Fused at the transformer? Unless you have the very rare single house feed arrangement in a domestic rather than industrial feed situation there will be several properties on one transformer output. For a good many years what has been done is not fuses, but fault protection relays that detect a range of probable fault conditions. This circuit is intended to open on a fault, give the fault time to clear then close, repeating a small number of time before not closing. However they are real pigs to set up correctly, are prone to a number of undetected faults, the two worst being failure to open on a fault, and the device failing to count. The open/close cycle (often called "machine gunning" for obvious reasons) can be very fast indeed, and can cause the transformer great distress.
Fused at the post top? Not too common on short street runs, but the fuse will be rated for fault currents below the cable current rating which is several times the individual domestic protection fuse. (Fairly common on long cross-field runs, particularly in windy areas.)
The trouble is a broken cable can start to arc well below the protective device trigger point, and once the arc is burning can sustain on even less current. I witnessed a high power, high voltage & current, fuse being tested - the test was a failure, the fuse ruptured at the right current, but not at the correct location, so an arc started, the initial applied current was in the region of 20kA, but once the arc was burning it dropped to a couple of hundred amps (with the voltage still up at 25kV), a very pretty green plasma flame, but very destructive as one can imagine. Thankfully there was a high speed camera in use and the fuse designer was able to see exactly where the fuse had started to rupture and change the some details on the fuse surface. I'm glad to say the second test with the redesigned fuse went very well.
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Message 108488 - Posted: 16 Jun 2022, 8:26:21 UTC - in response to Message 108487.  

The wire going into domestic properties is not designed to take more than 100A continuously. I know a few folk who wanted a lot of storage heaters and were denied them unless they got a bigger cable put in. Have a look at your incoming feed and estimate the conductor size.

When they do that the only component change, by the electric company, is the fuse, from 100A to 200A. The cable is not usually changed.
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Sirius B
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Message 108489 - Posted: 16 Jun 2022, 9:12:47 UTC - in response to Message 108488.  

When they do that the only component change, by the electric company, is the fuse, from 100A to 200A. The cable is not usually changed.
That's what happened with me shortly after relocating here back in 1985. Did not have to book an appointment for it as the power company itself (Eastern Electricity) were the installers of my storage heaters & on installation completion, up rated the main fuse.
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Message 108491 - Posted: 16 Jun 2022, 10:07:04 UTC - in response to Message 108489.  

When they do that the only component change, by the electric company, is the fuse, from 100A to 200A. The cable is not usually changed.
That's what happened with me shortly after relocating here back in 1985. Did not have to book an appointment for it as the power company itself (Eastern Electricity) were the installers of my storage heaters & on installation completion, up rated the main fuse.


A lot of people are getting their properties uprated to cope with rapid chargers for EV's now.
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Profile Gary Charpentier
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Message 108493 - Posted: 16 Jun 2022, 13:14:19 UTC

jeeze 100A wow. just think for a second. your bathroom heater, 10A maybe? think it will start a fire? maybe you better only deliver 1A to the house. Yes put a 1A trip on the transformer that serves half a dozen houses. Then its Peter safe.
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Profile Bill Freauff
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Message 108498 - Posted: 17 Jun 2022, 2:37:52 UTC - in response to Message 108493.  

jeeze 100A wow. just think for a second. your bathroom heater, 10A maybe? think it will start a fire? maybe you better only deliver 1A to the house. Yes put a 1A trip on the transformer that serves half a dozen houses. Then its Peter safe.


Nothing is Peter safe....
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Profile Dave
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Message 108504 - Posted: 17 Jun 2022, 5:03:23 UTC - in response to Message 108503.  

Why would you need a rapid charger for an EV at home? You charge it overnight. You only need rapid when you're out and about and want it done in 30 minutes while you sit in a café.


As someone who would charge an ev via a thirteen amp socket (outlet for those in US) during the day for free from my roof as most days I don't drive I can't answer your question but many need to upgrade even if they are only going to a 40A charger which is what many of the home ones go up to.
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Message 108506 - Posted: 17 Jun 2022, 6:19:13 UTC

Each property does not usually have its own cable to the substation. So if there are 20 properties connected via one cable on the same phase, what fuse rating would you suggest at the substation on each phase.
_____
Most homes have a 100A fuse because the normal domestic situation, without storage heaters of fast EV chargers, is two 32 A circuit breakers one for the cooker and the other for the 13A socket ring main, and two 16A circuit breakers for separate upstairs and down stairs lighting, and extractor fans. If the home uses gas for cooking then the 2nd 32A circuit breaker is frequently used for a shower fitting.
(2 * 32A) + (2 * 16A) = 96A

I have 200A supply because I had installed instant hot water heaters for the kitchen and bathrooms because too much energy was being wasted in the pipes unused. If you washed you hands in the furthest bathroom from the gas boiler more hot water was left in the pipes than was used.

______
My friend, who took over my position when I retired needs rapid charger because the distances to the furthest clients means he frequently gets home with less than 10% charge left. And goes out quite often in the evenings to do things for his 90+ year old Mum, plus all the normal; things people do
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