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.
