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Waka

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This is for the wiggly amp fraternity.

By mistake woodford sent me the table saw that contains the 5hp motor instead of the 3 hp.

I had someone around yesterday to look at wiring the machine and was informed that on initial start-up a 5hp motor will pull about 96 amps for a few seconds then dropping back to its normal ampage while running.

With the incoming electrical feed to the property protected by the standard 100 amp fure, there is a possibility of blowing the incoming fuse if anything else in the hiouse is using power.

I have spoken to woodford about this and they assure me that this machine will not pull that size of ampage on initial start-up.

My knowledge of wiggly amps is very limited, so the question is how many amps will this size motor pull on initial start-up?

Thanks
 

MikeW

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Hi Waka,

Not knowing how motors there are rated for certain, please do check this with someone who knows better!

Motors, in general, pull double the amps required to run steady-state.

So if a motor requires 20 amps to run, it will in general require 40 amps briefly to start.
 

Jake

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Most unlikely that the surge would be long enough to blow the fuse, I would have thought. But I'm no electrician. Try uk.diy for other opinions.
 

Midnight

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Whether or not it blows the fuse depends on whether the fuse is motor rated or not (see anti-surge fuses)... what it will do however is cause some serious light dimming until the motor's up to speed...
 

mudman

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Snigger.

Just got an image of Mrs Waka and friends sitting around the kitchen table having a wee sherry with the lights dimming and brightening repeatedly.

One friend remarks how the electricity is quite unstable these days. Mrs Waka remarks that "Oh, don't worry, he just has quite a large cutting list for this project".
 

Alf

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mudman":ongk0cbo said:
Snigger.

Just got an image of Mrs Waka and friends sitting around the kitchen table having a wee sherry with the lights dimming and brightening repeatedly.
Perfect conditions for setting up a seance. Just need to time the "one knock for yes, two knocks for no" to coincide with some hammering and Mrs W has potential for a whole business there. :lol:

Cheers, Alf
 

Waka

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Thanks for the replys guys and girls. al;l joking apart it was supposed to be a serious question, but I can see the the funny side of it.

I am reminded of the Yetties song "The Marrow" when the pub lights start to flicker. I'll probavley end up getting complaints from all of Weymouth as I draw the grid down.

Anyway not really had an answer to my original question, are all the wiggly amp experts asleep out there?
 

MikeW

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Waka":7dgvzd60 said:
...Anyway not really had an answer to my original question, are all the wiggly amp experts asleep out there?
Sorry Waka, sorta thought I had.

In the US the motor will be labled as to its running amps, sometime the start amps.

I have one 5hp motor. It requires 30 amps to run and 60 amps to start.
I have one 7.5 horse. It requires 40 amps to run, 80 amps to start.

Is your motor labled? Does the saw manual state its runing amperage draw? If yes to either, double the running draw and that shoud be the # required to start.

If that number AND the amperage drawn on either the combined service within the shop and or the combined draw for the line draw on the property, you will at least begin to weaken a fuse to where it will eventually pop, or as here in the states, will cause a breaker service to interupt service.
 

Woody Alan

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Waka

I am by no means an expert but have a very general background in the electrcal field. I think Tony is your man, doesn't he lecture in this very thing? Anyway a couple of generalisations. Firstly, your motor is likely to pull around 20Amps at most on steady run. Starting current 40 Amps ish for a split second, not several, rapidly falling to 20Amps (I suspect a little less).
You will possibly need a breaker rated for induction loads or peak loads so as not to trip straightaway. Breakers generally break at their rating. Cartridge fuses about 10% above and wired fuses at about twice the rating. As for blowing your incoming fuse unless your wife has a 5Hp washing machine she turns on at the same time it's highly unlikely :)
The only thing that may, and I mean may have an effect, don't turn on your extractor at the same time, wait 'til saw is up to speed or vice versa . One more thing your electric meter tails really ought to be up to it 16mm I believe maybe 25mm. More importantly if your workshop is down the garden like mine you really need a big a feed as you can get to avoid volt drop. I ran 16mm all the way down my garden. If you don't do this you'll get volt drop and your motor runs underpowered and loading will increase. Anyway this is "trying" to lower your worries. If you wait until Tony arrives he will pick up each of my points and give a more accurate answer.

Cheers Alan
 

Woody Alan

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Neil

I think you have something there. I don't think you can get as big as 5hp in single phase now you come to metion it. In which case ignore everything I previously said as I know nothing about 3 phase fusing arrangements.

Cheers Alan
 

Woody Alan

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This from the Woodford site

"Saw with 5HP motor, 30A/230V 1Phase 807 02 02 "

Apparently you can get 5Hp on single phase. I would think the 30Amp is starting current as I stand by my suggestion that 20Amps would be running current.

Cheers Alan
 

MikeW

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Once again exposing my ignorance of things electrical in general and for outside the US in particular, the amperage listed in the Woodford spec would be the running amperage...at least that is the way the specs are written here.

Have a good day all...
 
A

Anonymous

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Waka":1pgebpon said:
This is for the wiggly amp fraternity.

[/quote

I am from said fraternity - electrical engineer :wink:


By mistake woodford sent me the table saw that contains the 5hp motor instead of the 3 hp.

I had someone around yesterday to look at wiring the machine and was informed that on initial start-up a 5hp motor will pull about 96 amps for a few seconds then dropping back to its normal ampage while running.
This advise is incorrect as it is not that simple.

The start current is really dependant on the load as well as the motor type and winding. I have measured 5 times the full load current at startup on motors with a very large load.

I have also measured very small current at startup on small load of maybe 1.5 times FLC

Unless the load inertia is HUGE, then the startup current will be of VERY short duration (well under 1 second) and you will be fine if you use the correct fuse type.

The best course of action is to fit 'motor rated' fuses in the isolator feeding the motor. These are actually designed to accpet over-current for a short period of time whilst protecting the user, cable and motor during 'normal' operation.

you can purchase these fuses form any industrial electrical distributor in your area.
 

gwaithcoed

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Hi waka, I go along with Tony. Clearing away 50 odd years of cobwebs from my brain I recall

Current input of a single phase motor= H.P x 746 Divided by efficieny x volts x power factor

So as not to get too technical assume 100% efficient and a power factor of 1 we end up with, Current = 5 x 746 divided by 240 =15.54 amps
This is full load. Starting current will be about 6 times FLC giving you 93.25 amps.
But we are not starting it against a full load as the motor will only be turning the saw blade so as Tony says it will probably be no more than 1.5 times FLC

Go for it , give it a spin, if all the candles go out down the road, do as we used to do and tell them a spike had gone round the system


Alan [/u]
 

Waka

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Thanks all for the replys, I'm beginning to understand it all now.

I'm waiting for all the bits t arrive thenn the electrician will wire it all together. Unfortunately I'm back off to work on Tuesday so it's going to have to wait until August for the test run.

I did think of clamping an ammeter to the cable on start-up so that I'll know for sure wjhat it is going t pull. Atre these accurate?

I'll let everyone know the outcome when the start button has be pushed.
 
A

Anonymous

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Waka":2uf0vdsb said:
Thanks all for the replys, I'm beginning to understand it all now.

I'm waiting for all the bits t arrive thenn the electrician will wire it all together. Unfortunately I'm back off to work on Tuesday so it's going to have to wait until August for the test run.

I did think of clamping an ammeter to the cable on start-up so that I'll know for sure wjhat it is going t pull. Atre these accurate?

I'll let everyone know the outcome when the start button has be pushed.
Waka

Get a peak detecting clamp on ammeter if you can. These are what I always got my electricians to use when checking startup currrent on large motors.

The peak detect function wil record the startup current surge and hold it in memory
 

Argus

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Firstly there are EU rules about this, in addition to the UK wiring regulations.

If the machine is marketed in the EU it will have to have a CE mark by law. Your supplier has to give you a declaration of conformity, by law. This indicates that it complies with all relevant directives. There are a number that apply to woodworking machines, but the one we are interested in is the Electrical Magnetic Compatibility directive – EMC for short.

It governs and sets limits for electrical disturbance where the machine needs to be immune from external disturbance and within minimum emission limits so as not to disturb others. There are lots of tests that are relevant and as far as start current and network line disturbance is concerned the limits are in EN 61000 – 3 -3 and 61000 – 3 11.

It’s quite complex, but put broadly the start current impression on the supply network must be within the limits indicated in the standard, both as a current peak at start and as voltage reduction after start. The manufacturer MUST test and prove it. You, the end user, must not impose a flicker on the network as a result.

A 5 HP motor in the order of 3 to 3.5 kW. This is a large motor for single phase, but not excessively so. The penalties of a motor of this size on single phase as opposed to three phases will be loss of power (torque) and extra running cost. I would also check the power factor as a high power factor will increase your running costs.

For a motor this size, it is probable that the manufacturer has applied what they term conditional connection procedures.
This means that they declare that it must not be installed on a normal domestic supply (in the UK) rated at 80 amps. The may also give you limits on the supply impedance. If so, it must be installed on a minimum of 100 amp supply. You should see advice on this in the handbook.

If you have a true 100 amp supply, the odds are that you are on 3 phase anyway, or part of one.

Start current is dependent on a number of variables as pointed out previously. Temperature of the windings is one, as is the impedance of the supply and the limits in the standards are to test a warm motor. Broadly speaking a warm motor will draw about 5 to 7 times its rated current. A cold motor (i.e., the first start) will pull over 10 times, maybe more.

How long? The typical worst case is a reciprocating compressor that starts directly under load. The duration I have observed in tests on these is in the order of 4 to 6 electrical periods. That is 4 to 6 cycles, or about100 milliseconds. Correctly selected and rated fuses will with stand this easily.

So what are the problems?

Flicker. This can escape your property and affect other on the same network. It can make some people physically ill. The supply authority can in the worst case enforce a disconnection notice on you.

Lights dimming. This is a symptom of flicker.

Fuses blowing. Unlikely if you have robust enough installation.

Overload. Make sure that your installation and sub circuit that supplies the machine is man enough and the machine is adequately protected – in the UK rules, the fuse protects the cable, not the machine.

One last point. The UK rules on domestic electrical wiring changed in January this year. All new circuits fall under the building regulations and have to be notified to the local building inspector.

Very brief, but I hope this helps.
 
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Anonymous

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Argus":2nrc1fks said:
One last point. The UK rules on domestic electrical wiring changed in January this year. All new circuits fall under the building regulations and have to be notified to the local building inspector.
Apparently for those of us in the Norn Iron part of the UK these new regs do not apply yet, they will apply from Jan 2006. After that you must either inform building control or get it signed off by an approved electrician. This is not absolute gospel, however, my cousin is a wiggly amp technician and they are working their way through the rules and regs now.

Gareth
 

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