Getting a 110v transformer installed - basic questions

[Great_scot_selfbuild]

Hi all,

 

Short version: What’s involved in installing a 110v transformer? The yellow boxes I’ve seen on searches all have 3-pin plugs, but we’ll need ours a long way from our existing sockets; there is a mains cable yet to be connected up to where the meter is - do they get connected directly to it for the build phase?

 

We have mains electricity connection installed, but because of the site layout, the connection and meter is in the garage next to the road and I’ve been told we will need a 110v transformer next to the house (not that far away but using an extension would need quite a lot of length to keep out of the way of foot/vehicle traffic as it’s not a straight line between the two).

 

We have the mains cables etc installed in the ground that runs from the garage to where it comes out of the ground ready for the house and I’m just trying to understand how the electrician will install the transformer; it’s likely we’ll need it in place for a while and so I’d rather buy one myself and sell it on at the end rather than hire or have them loan one (in case we change electricians - hence asking here so that I have a good appreciation before discussing with them).

 

The garage has plug sockets in it and I’d assume in describing ‘connecting up a transformer’ this would connect to the cable coming out of the ground for the house, rather than running an extension cable - or is it really as simply as running the extension lead? (Just seems less safe and likely to get damaged or be a trip hazard, but happy to be corrected!).

 

Many thanks

[ProDave]

It won't just be the electrician using a 110V transformer, most trades will, and most will just bring their own and expect somewhere to plug it in.

 

So get or make a very heavy duty long 240V extension lead, or since you have the cable that is going to feed the house already buried, buy a waterproof cabinet and put a temporary site consumer unit in it with power sockets etc right at the house site.

[Nickfromwales]

1 minute ago, ProDave said:

It won't just be the electrician using a 110V transformer, most trades will, and most will just bring their own and expect somewhere to plug it in.

 

So get or make a very heavy duty long 240V extension lead, or since you have the cable that is going to feed the house already buried, buy a waterproof cabinet and put a temporary site consumer unit in it with power sockets etc right at the house site.

+1.

 

Running leads that far will be a liability. 
 

Also, it would need to be a larger 32a transformer instead of a regular 16a, as the second more than one trade plugged into it you’d be tripping the overheat cutout on it every 5 minutes.

 

You need 230v on site, as every trade will have battery chargers with them and will not want them out of site / mind, as batteries are expensive and ‘walk off’ quite regularly.

 

Hook the 230v up and get at least 3 metal clad double sockets installed for the duration, on a ring main fed from a 32a breaker in a local CU. 
 

Also, not sure what you’ve been told, but an electrician doesn’t “install” a 110v transformer…..you just simply plug these into a 230v socket?!? A 10 year old can install one , so don’t be paying for it!

 

 

[saveasteading]

6 hours ago, ProDave said:

waterproof cabinet and put a temporary site consumer unit in it with power sockets etc right at the house site.

Sounds best to me. Safer as no long trailing cables.

Plus I recall once having power provided  at a box 40m from the project, 110v transformers there then yellow cables to the building,  and drills were barely turning.

[Adrock]

14 hours ago, Nickfromwales said:

Also, not sure what you’ve been told, but an electrician doesn’t “install” a 110v transformer…..you just simply plug these into a 230v socket?!? A 10 year old can install one , so don’t be paying for it!

 

 

 

That's not true. If you're installing a 32A transformer it's not going to last long on a 13A plug top fuse.

 

On our sites, commercial admittedly, we install 10 KVA transformers. Those require installing by electricians

Edited Friday at 22:20 by Adrock

[Nickfromwales]

13 minutes ago, Adrock said:

That's not true. If you're installing a 32A transformer it's not going to last long on a 13A plug top fuse.

Incorrect. It's 110v so the maths change!

 

All the site trannys we've used (for 3 decades) have a 13a plug top, 16a or 32a. How else would you ever plug one in?

 

 

[Adrock]

5 minutes ago, Nickfromwales said:

Incorrect. It's 110v so the maths change!

 

All the site trannys we've used (for 3 decades) have a 13a plug top, 16a or 32a. How else would you ever plug one in?

 

Power triangle gives the following

 

 

 

110V x 32A = 3520W

 

3520W/230V = 15.3A

 

 

 

I've had those blow fuses quite regularly in the past, it'd need to be a decent draw go get that far though so I'll admit in most cases you won't have any issues because you'll never be at capacity.

 

The 32A plug rating is just that, what the plug is rated at, but you'd  not be able to utilise its full rating let alone both the 16A and 32A at the same time with any kind of decent load without blowing the plug top fuse.

[Nickfromwales]

Just now, Adrock said:

 

Power triangle gives the following

 

 

 

110V x 32A = 3520W

 

3520W/230V = 15.3A

 

 

 

I've had those blow fuses quite regularly in the past, it'd need to be a decent draw go get that far though so I'll admit in most cases you won't have any issues because you'll never be at capacity.

 

The 32A plug rating is just that, what the plug is rated at, but you'd  not be able to utilise its full rating let alone both the 16A and 32A at the same time with any kind of decent load without blowing the plug top fuse.

It's got a 13a plug though, hasn't it..... lol.😘

[Adrock]

And? I assume that's because they don't expect you to fully utilise the full rating of the transformer. You linked to a 3.3 and 5kva plug in transformer.

 

5kva at 230v gives you well over the rating of the plug top fuse, over 20A. I've also experienced them tripping 16A type C MCBs upon plugging them in over the years.

 

Anyhow, I'm being pedantic. Apologies. 

 

For the OP, you're right, stick a few metal clad sockets on a 32A RCBO and away you go.

[Onoff]

I'm core drilling and grinding at the mo off a 32A plug in trannie. Just done 1.3m through solid concrete at 102/107mm dia. Core bit was frequently sticking, amps ramping up and things getting hot. No 13A fuse popped.

 

 

[Nickfromwales]

10 hours ago, Adrock said:

Anyhow, I'm being pedantic. Apologies. 

No, we’re being pedantic, I don’t like to be excluded from anything ok. 

[Nickfromwales]

11 minutes ago, Onoff said:

I'm core drilling and grinding at the mo off a 32A plug in trannie. Just done 1.3m through solid concrete at 102/107mm dia. Core bit was frequently sticking, amps ramping up and things getting hot. No 13A fuse popped.

 

 

The damn things will run molten for a long time if it’s an overload tbf. 
 

I ran some electric UFH (in screed wire) off a 30m 230v extension lead to test it. 
 

After a few hours I went to check all was good. There was a little camp fire in the centre of the plug top, literally a molten pool with a small swirl of smoke rising off it, and everything still on circuit and floor warming nicely <2kw load iirc.

 

From that day on, the extension lead and plug were ‘together forever’, like Kylie and Jason lol.

 

I reckon you can get easily north of 16-17a before these actually start to think about popping.

[Adrock]

13 minutes ago, Onoff said:

I'm core drilling and grinding at the mo off a 32A plug in trannie. Just done 1.3m through solid concrete at 102/107mm dia. Core bit was frequently sticking, amps ramping up and things getting hot. No 13A fuse popped.

 

 

 

What rig are you using? Diamond drilling rigs probably don't get anywhere near 2000W.

 

13A at 230V is a LOT of power to be using continuously, you'll struggle to do that with one or even two tools on the go.

[Nickfromwales]

2 minutes ago, Adrock said:

 

What rig are you using? Diamond drilling rigs probably don't get anywhere near 2000W.

 

13A at 230V is a LOT of power to be using continuously, you'll struggle to do that with one or even two tools on the go.

If you take into account both the drill and  @Onoff then there were two tools in use lol. 

[Onoff]

40 minutes ago, Nickfromwales said:

If you take into account both the drill and  @Onoff then there were two tools in use lol. 

 

Enormous tools 😉

[Nickfromwales]

36 minutes ago, Onoff said:

 

Enormous tools 😉

Your missus said the 16a outlet would have been more than suffice  

[Onoff]

43 minutes ago, Nickfromwales said:

Your missus said the 16a outlet would have been more than suffice  

 

There's a joke there about a 5A plug in a 63A socket...

 

[Onoff]

2 hours ago, Adrock said:

 

What rig are you using? Diamond drilling rigs probably don't get anywhere near 2000W.

 

13A at 230V is a LOT of power to be using continuously, you'll struggle to do that with one or even two tools on the go.

 

Dunno, this wrist breaker! 

 

[saveasteading]

2 minutes ago, Onoff said:

this wrist breaker! 

Turn the speed down, don't press too hard and let the blade work. 

If I can do it, so can anyone. I did 4 of 150mm with one layer of mesh in an hour and no pain.

The drill was nothing special in weight or Watts, just smooth.

 

[SteamyTea]

1 hour ago, Onoff said:

this wrist breaker

Make a driller killer movie, and post it up.

[Onoff]

2 hours ago, saveasteading said:

Turn the speed down

 

It was on the lowest speed of 3 options.

[SteamyTea]

10 hours ago, Onoff said:

Just done 1.3m through solid concrete at 102/107mm dia

About 800 RPM then.

Which I think is about 4.5 m.s^-1.

Which is quite slow. If it was granite, you could go 5 to 6 times quicker.

[saveasteading]

10 hours ago, Adrock said:

1.3m through solid concrete

Have to admit that is impressive and might well hurt.

[Great_scot_selfbuild]

On 22/08/2025 at 09:54, ProDave said:

It won't just be the electrician using a 110V transformer, most trades will, and most will just bring their own and expect somewhere to plug it in.

 

So get or make a very heavy duty long 240V extension lead, or since you have the cable that is going to feed the house already buried, buy a waterproof cabinet and put a temporary site consumer unit in it with power sockets etc right at the house site.

Thanks - I should have made clear - it’s for all trades (we’re a way off from electricians having much to do on the house tbh and so it’s more for hte ring beam and timber frame build first.

 

I’d noted that the small yellow boxes have many comments advising that they’re not much use for more than a single tool in use. I’m not sure what the builder had in mind being ‘installed’ but I would guess something like these 10kVa (pic attached). I’ve not yet found detail on how these are connected?

 

Am I better off having a waterproof cabinet, consumer unit and sockets with multiple small transformers? (They’re far easier to pick up for not much ££).

 

 

 

[Great_scot_selfbuild]

On 22/08/2025 at 10:03, Nickfromwales said:

+1.

 

Running leads that far will be a liability. 
 

Also, it would need to be a larger 32a transformer instead of a regular 16a, as the second more than one trade plugged into it you’d be tripping the overheat cutout on it every 5 minutes.

 

You need 230v on site, as every trade will have battery chargers with them and will not want them out of site / mind, as batteries are expensive and ‘walk off’ quite regularly.

 

Hook the 230v up and get at least 3 metal clad double sockets installed for the duration, on a ring main fed from a 32a breaker in a local CU. 
 

Also, not sure what you’ve been told, but an electrician doesn’t “install” a 110v transformer…..you just simply plug these into a 230v socket?!? A 10 year old can install one , so don’t be paying for it!

 

 

Thanks @Nickfromwales we have lots of metal clad sockets for charging already and the people on site are all part of the same team at the moment. 

 

The challenge I’m trying to wrap my head around is where the builder would have this temporary connection positioned as the cable pops out of the ground exactly where it needs to rout up and into the plant room - if we install a temporary cabinet, CU and sockets there, then it’ll be right in the way. I’m wondering if a generator may still be needed if there’s plug-in tools needed until we at least have the cable up and in the footings of the house.