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Author Topic: Transfer Switches - cheap vs expensive?  (Read 2111 times)
DanielCoffey
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« on: January 28, 2020, 01:36:39 PM »

I have been asked by my electrician to select a 100A transfer switch to flip between UK mains and my small inverter which will be used during power cuts and I came across a HUGE difference in prices between what, on paper at least, appears to be a very similar product. Bearing in mind the adage "if it sounds too good to be true..." I would appreciate an opinion please.

Given a requirement of 100A, three position (1, 0, 2), two pole (single phase), what differences would you expect between the "seller branded" eBay switch of around £40 ex vat and a "commercial trade" website offering around £220 ex vat?

Both appear to be in similar hard plastic housings and the only outward difference is that the more expensive model seems to come with a lock on the selector.
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JohnS
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« Reply #1 on: January 28, 2020, 01:48:00 PM »

I am not an electrician, so this is only some thoughts.

Is the 100amp rating what can be switched under load or the maximum safe current that the switch can handle whilst not switching.

If it is the latter, you would have to switch everything off (probably via an isolation switch) before transferring.

This is probably not an issue as the switch switches off as you go from mains to generator and vice versa and thus it won't make much difference switching everything off.

Only my thoughts. 
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DanielCoffey
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« Reply #2 on: January 28, 2020, 01:51:58 PM »

My mains supply is on the usual UK 100A household fuse so will only ever encounter that rating if I was silly enough to turn on absolutely everything I owned. While there are lower rated Transfer Switches (such as 63A and 32A), the sparks advised matching the rating of the supply.

The only time this device will ever be switched is during or after a power cut and all circuit breakers will be off at that time anyway so there will be no huge inrush when power is restored.

The main concern I had was £40 ebay vs £200 trade supplier. What might I be giving up in the ebay switch for that large price difference?
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gravyminer
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« Reply #3 on: January 28, 2020, 02:20:46 PM »

hmmm

I was (actually still am ) looking at this option  and was going to let the battery bank voltage drive the switching.

but I never found anything as cheap as you are referencing.

I was looking at these -

https://www.ebay.co.uk/itm/ATS-Automatic-Transfer-Switch-Panel-1Ph-80A-AC1-Generator-Auto-Start-Output/321064248124

My electrician was nervous about the whole idea cos its not his area of expertise and talked about bad things happening as you switched.....

It may be that a manual switchover is a lot simpler though ?

The ATS options have the ability to fire up a generator, possibly giving a theoretically seamless option of mains -battery bank - genny.

Realistically though, unless you have mission critical needs like dialysis, a manual switchover for mains power failure makes good sense.
But how would you be treating the battery bank ?   Topped up with a floating charge from mains then crucified in a power cut or gentle regular cycling ?

I still have to work out the best way of creating resiliance without complexity .......


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gravyminer
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« Reply #4 on: January 28, 2020, 02:47:16 PM »

https://www.ebay.co.uk/itm/125-Amp-Changeover-Switch-240V-Mains-to-Generator-Transfer-Single-Phase-125A/272258677525?_trkparms=aid%3D555018%26algo%3DPL.SIM%26ao%3D1%26asc%3D20131003132420%26meid%3D8bb345afb8f64b4289ebe23d6ce4cf67%26pid%3D100005%26rk%3D3%26rkt%3D12%26mehot%3Dag%26sd%3D223622232450%26itm%3D272258677525%26pmt%3D1%26noa%3D0%26pg%3D2047675&_trksid=p2047675.c100005.m1851

Doesn't seem a bad option and it'll fit in a standard cu
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DanielCoffey
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« Reply #5 on: January 28, 2020, 04:07:58 PM »

In reply to gravyminer - I am only trying to provide temporary cover for essential low power items during power cuts in our rural area which happen every few months and have a duration of couple of hours to half a day. We have no self-generation and no fuel generator.

There will be a single 12V 210Ah (C20) Rolls AGM sitting in the cupboard very close to the consumer unit. There will be a dedicated circuit breaker off the board running to a 12V 30A AGM charger which will normally be off. Since the Rolls has a low self-discharge rate I will make a diary note on the first of every month to turn on the charger and open the utility cupboard doors to allow heat to dissapate. After the charger is done, it will be off again. In the event of an actual power cut we will switch off all devices at the board, turn on the 12V to 230V 200W inverter, flip the transfer switch and turn on the one sockets breaker. Considerable discipline will be required as we only have a budget of 200W before the Inverter shuts itself off for protection. That will allow us to run the NHS air mattress pump, community alarm box, phone and wifi for 24 hours before the battery is down to 50% DOD. By that time Scottish Power would already have offered to come round with a genny since we are on the Priority Services Register. They have been very supportive so far but it is a real bind crawling around and trailing extensions from the computer UPS and counting down the time before the mattress pump has to be switched off, hence the battery and inverter.

All installation will be done by a qualified sparks with approoriate cable thickness and fuses.
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oliver90owner
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« Reply #6 on: January 28, 2020, 04:30:03 PM »

Similar to JohnS, but bear in mind a change-over switch and an isolation switch may not be the same.

When I was working at a manufacturing process, the drives were all stopped and started by the ‘starter’ buttons.  The isolator switches were not able to start the drive and the contacts were not rated for disconnecting the load - only for carrying it, so they were only for isolation purposes after the drive was already stopped. A subtle difference.

If you are never going to change over while still taking power, the contacts can be of much lighter construction.

Number of switching operations is often quoted for devices.  Very occasional use is one thing, very frequent use might need something more robust.  Just remember the old adage - buy cheap, buy twice.  Choose carefully.
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JohnS
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« Reply #7 on: January 28, 2020, 04:34:51 PM »

Are all your 'essentials' on one MCB?

Perhaps have a separate circuits and mini consumer unit for your essentials and then put the change over switch between that and the main consumer unit or a Henley block from the meter.
That way, you can only supply your 'essentials' from the inverter.
Choose different socket face plates for the 'essentials'.
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gravyminer
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« Reply #8 on: January 28, 2020, 04:53:39 PM »

reckon you have the right approach Daniel although JohnS thoughts regarding a separate consumer unit that only feeds the essentials and the changeover switch just on that additional CU, makes good sense.

And Davelucks £18 manual changeover switch looks more than adequate.
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gravyminer
TT
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« Reply #9 on: January 28, 2020, 05:37:40 PM »

https://www.tlc-direct.co.uk/Products/CGM125CS.html

Nice and solid
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TT
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« Reply #10 on: January 28, 2020, 06:14:37 PM »

P.s. best to have the charger on a time clock to come on once a week for a defined period to combat discharging
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TT
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« Reply #11 on: January 28, 2020, 06:18:42 PM »

A changeover switch breaks the DNO supply before making the ‘inverter/generator/alternative’ supply

Get a volt stick pen that beeps when in close proximity to the mains cable, and position it next to the DNO cabling, when power is restored, it beeps away altering you that you can go back on mains.
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bxman
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« Reply #12 on: January 28, 2020, 06:36:09 PM »

Unless I have got the wrong end of the stick.

the change over switch is only going to be switching the output of a 200 watt inverter
 
on to a dedicated plug / circuit  
That will allow us to run the NHS air mattress pump, community alarm box, phone and wifi for 24 hours before the battery is down to 50% DOD.


It is never going to do more than 200 watts   so what on earth does it need to have a 125 amp switch for a  5 amp change over switch will be more than adequate  .

you will not be actually switching it when carrying current in any event as far as I can see.

  
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Iain
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« Reply #13 on: January 28, 2020, 08:05:29 PM »

Hi
For safety I would be very tempted to run a separate circuit for the items to be used on the inverter. That one circuit could then be switched to be fed from the inverter.

(I have run a separate circuit for my emergency circuit in my house.)

It would then be foolproof, there would be no chance of anything else trying to power up on the inverter if a MCB was missed when isolating the other circuits.
I would be very surprised if the electrician would wire in a system that "could" in theory allow the whole house to be left switched to the inverter.

Iain
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