Newbie PSU calculations

[dazp1976]

Once you go over 13A in the UK, there is no fuse inside the plug. And even a nominal 13A fuse will sustain a lot more than 13A for extended periods before finally clearing. For instance, the std UK fuse cartridge would likely supply 26A indefinitely and the ring main behind the socket (typically a 30A type B) would also be happy to supply 50% over nominal almost indefinitely.
http://wiki.diyfaq.org.uk/index.php/...FusingTime.png
https://electricalapprentice.co.uk/h...t-mcb-or-rcbo/

Ideally you'd have a large incoming MCB and smaller, individual MCB circuit breakers for the different circuits inside the cabinet anyway. Like a big one for the VFD and smaller ones for the servos, control circuits, external coolant pump etc. This also allows you to isolate them during testing etc.

The function of the MCBs is to protect the wiring (and you) from fire risk etc during a fault, while allowing unimpeded operation otherwise. If you simply relied on one large MCB for all of the mains circuits, you could have a nasty fire / shock unless you use the same big fat wiring everywhere, including all the protective earths. Even then, the safety insulation used in transformers, power supplies, VFDs etc should be protected against large fault currents to maintain their integrity during a fault condition.

When it comes to a DC power supply for steppers etc, say example a switched. We'll go a little overboard here.
Lets say you have a 60Vdc, 16.6A, 1000W big unit. This is it's max OUTPUT.
It doesn't mean that it uses 16.6A from the mains and needs a breaker.
You're INPUTTING 240Vac to it, so 1000W on 240Vac is actually 4.16Amps.

If you're building a control box with these types in you'd prob only want a 6A or 10A for the above size supply.

You don't see a 1000W heater or toaster or kettle needing a MCB.

Something like that anyway.

[m_c]

When it comes to a DC power supply for steppers etc, say example a switched. We'll go a little overboard here.
Lets say you have a 60Vdc, 16.6A, 1000W big unit. This is it's max OUTPUT.
It doesn't mean that it uses 16.6A from the mains and needs a breaker.
You're INPUTTING 240Vac to it, so 1000W on 240Vac is actually 4.16Amps.

If you're building a control box with these types in you'd prob only want a 6A or 10A for the above size supply.

You don't see a 1000W heater or toaster or kettle needing a MCB.

Something like that anyway.

And you totally missed the point Muzzer was raising.

Plus it's not like it's not unknown for heaters, toasters, and kettles to go up in flames.
Just because the accepted default fuse size is 13A, doesn't mean it's the ideal size to use.