Cost to convert to 3 phase

[Random Orbital Bob]

Has anyone recently had their workshop converted to 415V 3 phase and if so what was the cost please?

Many thanks

 

[deema]

Hi Bob,
Had a 100A/ phase 3ph installed about a year ago. 60M run from the pole. It was c£9K. The biggest variable I found was if they needed to add a new transformer or whether they can tap off an existing one. I also had to pay for them to dig across a road. The bits I was allowed to do - trench lay the pipe they supply and back fill on my property - I had done myself.

 

[Phil Pascoe]

I had my old one done about five years ago. It was £750 - but the mains were only three feet away.

 

[mbartlett99]

Not sure if this is helpful or not but I have 3 phase into the house - always wondered why. When the guy came to fit the new meter I asked him - apparently its quite common in country properties renovated in the 80s. My house isn't 3 phase - the two others are diconnected but you never know you might be lucky.

 

[RobinBHM]

I understand the major hurdle is dealing with the utility company, apart from the cost.

 

[HappyHacker]

I was quoted £600.00 to put a three phase supply to a new house but they were replacing an overhead cable at the time before it pulled a pole over and the re was only a short run (20metres) from a pole.

From conversion with electricians in other parts of the country the different utility companies and even different parts of the same utility company have different levels of service.

I have had excellent service from Scottish power.

As Deema has said if they need to upgrade a transformer you can end up paying for the cost of upgrading it which any future customers then get for free.

It is free to get a quote so go for it and ask if there are any things you can do to reduce the cost such as digging and backfilling the trenches. The forms you need to complete can be a bit daunting though.

 

[Farmer Giles]

I was quoted 22K plus for a 3 phase supply so I bought a 10hp 240 to 415v PWM inverter whole workshop supply. It has soft start which helps with inrush current, and I put a 50A type C MCB in the distribution board to feed it.

I only use one machine at a time, at the moment I just run cables back to a central socket so only one machine can be plugged in, it runs my 7.5hp lathe fine, and my 20+ cfm compressor fine too. I will wire it to a switch at some point that makes sure only one machine runs at a time is used. The lathe has a 3 phase motor for suds and that does run at the same time as the main motor but is only about 1/4 hp.

It came from Drives Direct, I think it was between 1200 and 1500 inclusive 2 years ago, its a big lump, came on a pallet. Much quieter than the old rotary converters It comes ready to go with 3 phases and neutral just needs input wiring in, it has a standard 3 phase socket fitted. Mug to show scale, it had no liquid in it!

Cheers
Andy

 

[Phil Pascoe]

. Mug to show dimensions, it had no liquid in it!
I think most of us know what size a workmate is. :lol:

 

[Farmer Giles]

. Mug to show dimensions, it had no liquid in it!
I think most of us know what size a workmate is. :lol:

Doh! I guess it was pretty obvious from the first shot

I still use the odd VFD for machines where I want speed control and I'm too lazy to move a belt

 

[Random Orbital Bob]

Thanks for that chaps. My enquiry is to consider the options for powering a 7.5HP spindle moulder in my currently single phase workshop. I would also be extremely unlikely to be running more than one machine at a time (unless I upgrade my DX to the size that needs 3 phase). So it sounds, just looking at the helicopter view, that going the utility company, full conversion route is deathly expensive whereas the chunky inverter route is cheaper and very do-able. Would you say that sounds right?

 

[graduate_owner]

Just wondering, what are the running costs when you have a 3 phase supply installed? Is there an increased standing charge, and do they consider you to be commercial and so charge you 20% VAT on the bill?

K

 

[Farmer Giles]

If you went the inverter route and it didn't suit you then I guess there is a resale value so you could recoup some of the money. My quote was 22K because they would have had to change the transformer so I would get a quote first before deciding. G_O's query on standing charges and VAT is also interesting.

Only issue I have had in 2 years of occasional use is a 200mA slow blow protection fuse blowing, I phoned them up and they diagnosed it over the phone and apart from me not having a fuse handy it would have been up and running in minutes.

if the costs were similar I would go for the full 3 phase supply, just less to go wrong and no issues with your compressor accidentally kicking in while your using your spindle moulder. It wouldn't damage the inverter, but would just be annoying.

 

[jackjohnsonuk]

Rob,

Dealing with 3 phase supplies for Temporary Building Supplies at work all the time they vary from 1.5-10k generally. I'm pretty used to putting in the applications though so and it wouldn't cost you anything to find out, just give me a shout if you want a hand!

At around 5-6KW I personally would look at rotary, not a static inverter so you'd probably get one supplied for about £2k. By the time you run a new circuit from Consumer unit to the inverter your material cost will be roughly £2.2k I would think (depending on where your consumer unit is). I'd be more than happy to help with the labour so you wouldn't have to worry too much about that bit.

Then the last spanner in the works would be what size single phase supply you have. From memory, I think your draw on a 7.5hp motor would be about 30-40amps, most house supplies are fitted with an 80amp main fuse so just check that too.

Personally, i'd get a quote first and go from there, an inverter is always the second option in my mind

Good Luck

Jack

 

[dickm]

A near neighbour asked to have 3-phase installed to run his heat pump (I always said they were a nonsense!) and the supply company quoted something very cheap, which he accepted with alacrity. Only then did the suppliers apparently realise that the transformer directly across the road from his house was only single phase - doh. They tried to sting him for about £10k to cover new box and wires from the supply across the field, but he stuck to his guns and made them honour the original quote. Mind you, it meant that all of our road was off power for most of a day while the company took their time over installation!

 

[graduate_owner]

Apart from cost issues, there are other things to consider. An inverter gives you variable speed which is pretty useless for, say, a compressor but excellent for woodturning. It also has a resale value, but then it could be a problem if it went defective. Mains supplied 3 phase may not add value to your property if you move, so perhaps no 'resale value.' Mains 3 phase however is a true, balanced 3 phase and not an approximation. I don't know how good rotary converters or inverters are at simulating 3 phase, but I do know that static converters are a very rough approximation and you only get about 2/3 of your motor power.

K

 

[jackjohnsonuk]

graduate_owner your total right in your comments, and just in case it helps anyone else a rotary converter does give the machine the full beans by a nifty trick using something known as a donkey motor. Both static and rotary have their advantages and disadvantage, and I can be really boring explaining it if people want me to?

However always remember any three phase motor will technically run on single phase if your start it by hand... it won't run very long before it burns out mind you but all these clever systems are doing is interrupting the 'usual' single phase sine curve to introduce two slightly off-beat ones to make the three phases

And if anyone pockets are feeling particularly deep VFD's (Variable Frequency Drives), also known as inverters, are the Festool of the Three Phase Generation world, however, currently these are at the lower end of the HP/KW spectrum so in this case not applicable.

 

[graduate_owner]

I bought a 2.2kW VFD, not a far east import, cost me £175 ish, it's an Invertek, UK made, sold by Willpowerelectricalltd on ebay. I think they cost around £225 now. An affordable solution as far as I was concerned. A 4kW version costs about £380 so again affordable when compared to a 3 phase installation. The only thing to watch out for is some ( including mine) are IP 20 rated so need to be mounted in a dust etc proof cabinet. IP 66 versions are almost twice the price.

When using VFDs, for those new to the devices, you need to be aware of:-
1. The motor needs to be controlled directly by the inverter, you can not use the switchgear of the lathe or whatever. This was an issue for me with my colchester, and I ended up buying a rotary inverter for that.
2. If you slow down the speed of the motor you kay lose torque, depending on the settings of the inverter's parameters.
3. Slowing the motor also slows the cooling fan so you might cause the motor to overheat if you use a very slow speed. I was thinking about inserting a suitably placed, separately powered fan by my motor to compensate for this.
4. Unless you spend considerably more for your inverter, your motor must be dual voltage so it can be connected in delta configuration, not star, and will run on 220v.

As Farmer Giles said, you can get whole workshop solutions providing 440v output. Out of my price range though.



K

 

[beech1948]

6 years ago I had a 3ph supply added to my workshop. Cost was £900. 3ph supply was under the pavement and trench length was only 8.5 ft. Dug and backfilled my own trench.

In my new house for 9 months and 3ph supply is 35ft and cost looks like £1700 so going with VFDs.

 

[Farmer Giles]

The inverter I have is not a VFD, it simulates 3 phase pretty well and you can use the original switch gear. It's 10hp, and is quieter and cheaper than the equivalent rotary converter. With the soft start feature it minimises inrush and works off a 50 amp breaker. It only needs that kind of current when on full load and I have no issues with it sharing the house supply when the washing machine, dryer and dishwasher are hard at it.

I would still go for a proper 3 phase supply if it was cheap enough but it comes a close second

 

[wallace]

I run a lot of 3 phase machines via a cheap 5.5kw transwave static converter. My machines are big boys as well. It will run my 30", 18 planer and big blocks on the spindle moulder. I do have to have another 3 phase motor idling to improve the quality and starting torque for the big stuff.
Unless your running something like this big sander https://www.youtube.com/watch?v=OWZhJmLK6fE which my little static struggled to get spinning I think a full 3phase supply would still take a while to get it moveing