Used Lathe Pinnacle PL1340C Gap Bed

And to let you understand Dave, i am not planning on having a lot of people working here, maybe 2 or 3 in the future so the loading on the supply shoudln't be an issue, maybe 2 machines max at any one time and that would be unlikley. its just i am trying to plan out what i will end up with and what i could need so as not to go down the wrong route and regret it at a later date.

Hi Robert. Have you tried posting on the commercial electrical forums. You may find that there will suitable posts to help with your problems. If I were thinking of setting up an electrical system for an engineering business, that is where I would start.

Some where like Link should have up to date info/rules/regulations/practical installation tips. Also a word with your supplier should garner all the info you need.

We seem to have drifted away from "what do you think of this lathe" to "how can I wire up and run a complete engineering shop with several machines with a less than perfect power supply"

As great as this forum is and its great & helpful members I feel that in your position I would want some facetime with the power supplier and the local electrician who is going to do the installation or sign it off for you.

regards

Yep, it's all about the planning. But I've probably not made my point clear. The issue with any scheme is whatever the bottlenecks are.

My bottleneck is living within the constraints of an ordinary domestic supply, ie 240V single phase and 13A plugs and sockets. Your workshop has considerably more oomph, but being constrained to either 240v single phase or 480V single phase is a bottleneck.

480vac single phase isn't commonly used for powering machine tools, so any solution involving it is likely to be a bit weird and therefore expensive. Another bottleneck.

240Vac single phase is common as muck and there are lots of phase converters available. VFDs are 'best because they're small, quiet, efficient and provide speed control', but they have limitations, partly because they are intelligently tuned to the load:

• Several inexpensive VFDs, one per motor, is fine but the cost adds up.
• 230Vac to 400V 3-phase is available but not common. A small problem fixed by moderate £.
• Inexpensive units are only intended to drive one motor. Although they can be shared the set-up is troublesome and inefficient. Inability to share is a blocker.
• Smart plug anything in at any time VFD's exist, - they're used in the MW range to emergency power hospitals - but I don't know of any small inexpensive ones. They may exist.
• Large motors need expensive VFDs.
• Inexpensive VFD's can't cope with two-speed motors.

The other phase converters have disadvantages too, mostly inefficiency, poor phase balance (if that matters), or noise.

• As capacitor type electronics are really stupid they won't have a nervous breakdown when an odd load like a two-speed motor or another device is plugged in, but it may be necessary to change switch settings to get them to perform. How well these work 'depends'. Usually people get on OK with them, sometimes not. If phase imbalance is a problem, it can usually be improved by adding an idler motor - more fuss and money, but perfectly do-able! Bottlenecks rather than showstoppers.
• Rotary converters do a good job making balanced 3-phase and are load tolerant. On the downside, they're noisy, inefficient, big and expensive. Just a guess, but I suspect a large one of these is your best bet. Something chunky enough to keep 3 people going!

On the subject of cost, say you employ yourself and two young men at National Minimum Wage £8.20 per hour, and you all do 140 hours per month. That's £3444 per month, or nearly £45000 per year. Plus rates, tax, heat and light, pensions and other overheads. If bottlenecks due to power problems reduce output by 10%, it takes about 5 years to marginally justify spending £25,000 on proper 3-phase. If bottlenecks reduce output by 20%, laying in 3-phase early is definitely a good idea. Otherwise you pay people to stand about waiting!

Just an illustration. In practice your business may not depend at all on keeping workers and machines busy. But efficiency would be mission critical if the business depended on doing lots of low profit machining quickly.

Apologies if you know all this already - it's just I was trained at work to be alert to requirement creep and financial optimism. Even the professionals get it wrong - dare I mention HS2?

Dave

Robert

Although the fuse carriers on your main DNO fuses may be labelled as 100A , you would be advised to check what current you can actually take from the network. I used to work at Electricity North West and the maximum supply capacity there was specified as 20kVA for a single phase supply ( ie 80A). The other issue may be that the rating of the pole mounted transformer may be a limiting factor. Also there are limits on voltage fluctuations caused by motor starting currents or welders (see ENA ER P28).

Stuart

Robert

have you got the lathe yet?

I guess once the lathe arrives it will be a few weeks before installation is completed. Be nice to know it got there safely though.

Nothing to do with Robert's problem but out of idle curiosity I took some photos of a local installation which I believed to be split phase. Except looking at them I don't understand the wiring! May be due to missing details because the photos were taken with a zoom lens across private land, or because I don't know about power distribution!

The consumer is a farmhouse and outbuildings converted to four or five private homes. Power comes from a HV transformer on a pole about 100 metres from the buildings, and the LV feed is buried.

The HV end of the line is connected to the grid about 750 metres away:

The two wires on the left obviously take a single phase to the farm. The three wires on the right are incoming, and the cross-bar beneath takes 3-phase across a road to power a Sewage Farm. (Rural charm!) Anyway, it's clear that the farm only gets one HV phase. There's no earth or neutral.

Just outside the farm the two HV wires drop to a pole mounted transformer:

On the transformer's side can be seen 4 insulated terminals, which I guess go to two secondary coils. Although 3 wires are connected, (implying split phase with a centre-tapped neutral), the two straps suggest the secondaries are in parallel, ie single-phase to the farm, with one side earthed and neutral under the pole.

The wiring around the fuse doesn't help me much:

Again 3 wires are involved (four including the poles safety earth), but I can only see one fuse. Possibly there's another fuse hidden on the other side of the pole.

Does any of the wiring make sense to you Stuart? (Or anyone else!) Is this split-phase, or just plain single phase? Also, is the HV side 6kV or 11kV? I guess 6kV because the poles and insulators feel safe for lower rather than higher voltages, but it's just ignorant gut feel.

I've got a few books that explain power distribution theory but none explain how it's done in practice in the UK. (I feel like Sheldon in the Big Bang Theory; when Penny's car breaks down he understands thermodynamics, but has absolutely no idea how to fix a real engine!)

Dave

Edited By SillyOldDuffer on 23/05/2020 10:36:36

Dave

It’s single phase.

This design of transformer has 1 HV winding and 2 LV windings as you thought. It is a type that can be connected as single or split phase by changing the links you can see. As this one is connected, the 2 windings are connected in parallel. The 2 terminals on the left are the live phase connections in this case, and the 2 right hand terminals are the neutral. If the 2 links were removed and only one of them connected across the top 2 terminals, this would be the neutral and the bottom 2 would then be the 2 live split phases. It is difficult to see the earthing, but the LV neutral will normally be earthed separately from the HV earth which is just used for the transformer tank and other metalwork.

The HV voltage could be either 11kV or 6.6kV, the design and construction are the same.

Single phase or split phase transformers are connected across 2 of the HV phases.

Three phase transformers have a delta HV and star LV with the star point the neutral which is earthed at the substation.

Stuart

Brilliant answer Stuart, I'm a little more educated now. (Two of three more facts and I shall promote myself to 'expert', hollow laughter.)

There's a similar arrangement a long walk across the fields I might be able to photograph later. As it only serves a biggish house and a second-hand car business, I bet it's simple single phase too.

Many thanks,

Dave