Single Phase Dol Starter

[Manator]

I seldom follow wiring diagrams, most machines I wire are 3 phase so its a simple L1, L2 and L3 connect. I have to wire some single phase DOL starters, no problem, I normally just link a phase through and connect the motor output through the other phases. However these days I am confused because some of the wiring is done internally.

The link through could be live (Line) or neutral, does not make that much difference TBH as long as all three poles are monitored on the overload.

The wiring diagram I have from Schneider shows the start push button being wired from the neutral, I have always found this to be a little strange, I have witnessed flashing when using a neutral for switching.

I prefer to use the phase wire for the switching,the stop is on the overload so no wiring involved.

So if I use Line for the switch do I wire from 95, or 14? Or do I just wire it up as I know it should be?

 

[Kurt]

The neutral is only there for 240V coil. From memory because of the internal connection it does not lend itself to putting A2 direct to neutral in the classic sense , happy to be corrected but think that's how it is

 

[Evans Electric]

Never known the Neutral used as the control circuit TBH , usually do  N in to (1)  --out on (2)          L in to (3)   link from (3) to (5)  & out on (6) 

 

[Davethsparky]

I was told at college that N is always used for the control circuit in a single phase DOL, but I can't remember the reason. Though if I remember correctly it does work out simpler for some reason.

 

[Sidewinder]


IMHO.


N is whilst a live conductor it is an earthed conductor.


Now I do not believe that a DOL starter is "really" "under" BS7671.


It is "under" 60204.


Now, in a metallic enclosure, with the N as the control circuit, and earthed, then a single fault would be a fault to danger.


As 60204 requires control fused protection, then how can you use a fused earthed conductor as the control?


In fact, there are a limited number of scenarios under 60204 that even allow the control circuit to be "fed" "directly" from the mains supply.


This has been relaxed somewhat, however, personally I don't like the relaxation, I preferred the original specification as it was much safer, and as it is the control circuit that the operator interacts with, then safety is the most important.


 


Do your design FMEA's on the potential failure modes of the original & your modified design, then do which ever turns out as the safest.


I suspect I know which one will be the safest.

 

[Manator]

That is what I was getting at Sidewinder, the wiring diagram clearly shows the neutral as the control wire which goes against all my gut feelings.

What I normally do is take a line through L1 out of the overload and into L2 then direct to the motor, the neutral in through L3 and direct to the motor so all three lines are monitored for overload. I always switch on line not neutral.

 

[Tony S]

From being an apprentice it was drummed in to me “no control contacts on the neutral side of the coil”.

An earth fault on the neutral side would go undetected until you needed the stop button.

I blame the Americans for it. In the thirties they couldn’t get journey men with experience of control wiring and so they “simplified” the wiring. I can’t see how they work that one out, it’s more complicated to me.

 

[professional]

The Italians used to take some beating. Their old system of requiring contacts to close to energise a coil to STOP a machine was frightening - especially on vibrating machinery with all of those loose connections after transit from the continent .... 

 

[Evans Electric]

N as the control circuit !! Thats never right surely ?      Put a feed on the coil & switch the N side ....come on !!  ?

As the Paddler says .... rewire it properly .

The old GPO  ( now BT)   engineers , when designing stuff for their buildings used to do stuff like that .

You'd get a wiring diagram from them , done by telephone system engineers....I used to have one left  , if its there I'lll post it .

I think it was for some heating ...follow the circuit round & when the humidity stat operates , theres a dead short to neutral as I remember.   

Their COW said their " 50V electricians" had designed it.

 

[Manator]

I had 5 to wire up, I did not follow the diagram I just wired them as we know better. They are all installed and working properly switched on line and not neutral.