One for electricians/engineers

[wrightclan]

I have a couple of electrical questions with regard to my planer. I have a multico planer with a 2hp Clarke motor and a 10-16 amp starter switch (set to 10 amp.) It has been periodically blowing 13 amp plug fuses on startup (only ever on startup i.e. never due to taking too heavy a cut.) It seems to happen more frequently in cold weather.

My first question. Shouldn't the starter switch (as I understand it basically a 10-16amp MCB--set at 10 amp) trip before blowing the plug fuse?

I've been planning for some time to hardwire it to a 16amp MCB in my consumer unit. Finally yesterday, after blowing several fuses in a week, I bit the bullet and did exactly that. It's up and running fine, but in the process, I came across something else I don't understand.

The consumer unit is a split load, with three outdoor circuits protected by an RCD. I initially wired my 16 amp circuit into the non-protected side. But as soon as I switched on the planer, it tripped the RCD? I checked all my wiring both visually and with a continuity tester. Everything seemed fine, but it kept tripping the RCD (again I was reasonably sure that MCB was unprotected by the RCD.) Finally, I moved it over to the protected side, with the outdoor circuits, and everything is working fine. What's going on? Your advice would be appreciated.

Brad

 

[Adam]

Don't forget on a split board the neutral is split - you didn't wire it to the RCD side neutral having installed it on the non-RCD live side?

Adam

 

[wrightclan]

Don't forget on a split board the neutral is split - you didn't wire it to the RCD side neutral having installed it on the non-RCD live side?

Adam

Possibly. :-k I'll' look at it.

Brad

 

[wrightclan]

Don't forget on a split board the neutral is split - you didn't wire it to the RCD side neutral having installed it on the non-RCD live side?

Adam

Possibly. :-k I'll' look at it.

Brad

Yes sir, that's exactly what I did! #-o Thanks, Adam. =D>

Now if someone could answer why the starter wouldn't trip before blowing a 13 amp plug fuse? Just to satisfy my curiosity. Don't think I'll be switching back.

Brad

 

[Adam]

I have a couple of electrical questions with regard to my planer. I have a multico planer with a 2hp Clarke motor and a 10-16 amp starter switch (set to 10 amp.) It has been periodically blowing 13 amp plug fuses on startup (only ever on startup i.e. never due to taking too heavy a cut.) It seems to happen more frequently in cold weather.

Peak current demand is at startup, not on heavy cuts. Say your peak at startup may be double the normal running current, but it only lasts a fraction of a second normally.

My first question. Shouldn't the starter switch (as I understand it basically a 10-16amp MCB--set at 10 amp) trip before blowing the plug fuse?

I'm getting confused on your terminology of starter switches. MCBs are tolerant of small overloads and current surges - but are designed to trip quickly under fault conditions. Overloads of up to 150% which are only brief will not trip. Something lasting longer tens of seconds but only a marginal over current will trip it. So its unlikely that you peak startup current will cause a problem to your MCB but will burn out a 13amp fuse. You would be best with a larger rated output.

Adam

 

[Adam]

Yes sir, that's exactly what I did! #-o Thanks, Adam. =D>

No probs. Please it fixed it. As you can imagine, when the RCD finds 10 amps of current coming out its neutral that it doesn't see coming out the live side - it'll trip instantly.

Adam

 

[wrightclan]

I have a couple of electrical questions with regard to my planer. I have a multico planer with a 2hp Clarke motor and a 10-16 amp starter switch (set to 10 amp.) It has been periodically blowing 13 amp plug fuses on startup (only ever on startup i.e. never due to taking too heavy a cut.) It seems to happen more frequently in cold weather.

Peak current demand is at startup, not on heavy cuts. Say your peak at startup may be double the normal running current, but it only lasts a fraction of a second normally.



Adam

Well, I only mentioned heavy cuts, because I have blown fuses with my 2hp tablesaw (very infrequently) by taking heavy cuts with a dullish blade, but never at startup--exactly the opposite of the issue with my planer.

Brad

 

[wrightclan]

My first question. Shouldn't the starter switch (as I understand it basically a 10-16amp MCB--set at 10 amp) trip before blowing the plug fuse?

I'm getting confused on your terminology of starter switches. MCBs are tolerant of small overloads and current surges - but are designed to trip quickly under fault conditions. Overloads of up to 150% which are only brief will not trip. Something lasting longer tens of seconds but only a marginal over current will trip it. So its unlikely that you peak startup current will cause a problem to your MCB but will burn out a 13amp fuse. You would be best with a larger rated output.

Adam

My particular starter switch (Clarke) has what appears to be basically an MCB inside. Your explanation helps. Thanks again.

Brad

 

[Quetech]

You should probably be using a type c mcb as these are designed for motor circuits.

Mike

 

[paulm]

Type C mcb's are more tolerant of start up surges and are better than the standard type B mcb's for this kind of application I believe, though not a sparky so would check for yourself to be sure.

Cheers, Paul.

 

[DaveL]

A note on start up currents, the 3HP motor that I fitted to my Wadkin draws 13.5 Amps on full load, but it will take 3 times that on start up when its just spinning up its self and the blade, no load. :shock: This was from the data the manufacture lists, there are a number of different types of single phase motor and the start up current does vary between them.

I also have a Multico planer, with a 2HP motor, I had to fit a 16 amp plug on it as it always blows a 13A fuse on start up. :roll:

I have 'C' type breakers in the board for the 16A sockets in the shop.

 

[shockingmoment]

could it be that the 10A breaker inside the starter switch is in fact a thermal overload unit? these devices trip only after sustained overload currents. the amount of time will depend on the overload. fuses / breakers protect against short circuit currents primarily. overloads protect the motor.

the hint you gave is the 10-16A adjustment. breakers are usually fixed. thermal overloads are adjustable