Trouble shooting?

[FrankUK]

I do a lot of commissioning and trouble shooting for a well known name of ventilation/heat recovery equipment, and I was tasked to have a look at a problem in Bournemouth today, where the fault was reported as an electrical heater 'overheat' problem.

The ventilation unit has an inbuilt supply fan and extract fan, heat exchanger and electric heater battery. The unit is 3 phase with inbuilt controller.

Here's the pictures of what I found. The additional wire terminals (not the manufacturers grey ones) have been fitted by the installing electrician, who has taken a supply to feed the orange relay which switches the additional ventilation fans on when the unit is running.

K1 is the contactor for the supply fan on full speed

Anyone spot what has happened?

 

[benji]

are we seeing enough of the drawing to find the problem?

 

[Stuuk1]

Haha I love this kind of thing!

 

[Darkwood]

Im puzzled a bit as you say it was reported as an electric heater overheat which would suggest airflow loss, now this system should have air flow senses to shut heater off long before it overheats but thats another issue as i said i cant see the way the system works and thus not sure what and when which motors and heaters should be active and when not... its easy to see a fault if your familiar with how the system works in the first place. I feel the way you have presented the thread means we are probably overlooking the obvious but can you tell us how the system would normally work and what fans should be on or off when heater bank is needed?

All i see is if K1 or K2 are not closed then the orange relay cant pull in but again you supplied partial info and want us to pick the relevant parts of it.

 

[Darkwood]

Stuuk1 ..... what was your other post on about... where is the Star/Delta timer or even the set up for star delta?

 

[FrankUK]

Im puzzled a bit as you say it was reported as an electric heater overheat which would suggest airflow loss, now this system should have air flow senses to shut heater off long before it overheats but thats another issue as i said i cant see the way the system works and thus not sure what and when which motors and heaters should be active and when not... its easy to see a fault if your familiar with how the system works in the first place. I feel the way you have presented the thread means we are probably overlooking the obvious but can you tell us how the system would normally work and what fans should be on or off when heater bank is needed?

All i see is if K1 or K2 are not closed then the orange relay cant pull in but again you supplied partial info and want us to pick the relevant parts of it.

You are on the right track...you just need to look a little closer at the details posted....(K1)

 

[Darkwood]

Well only other thing K1 as you have stated is intake fan full speed and all i see on the output is the loop to K2 and 2 wires one of which goes to signal the speed controlled fan so i can hazard a guess its lost control of the intake fan and is now pulling in a speed controlled unit which if set at low speed which will allow for overheating on heater bank if set to run slow.

 

[FrankUK]

Well only other thing K1 as you have stated is intake fan full speed and all i see on the output is the loop to K2 and 2 wires one of which goes to signal the speed controlled fan so i can hazard a guess its lost control of the intake fan and is now pulling in a speed controlled unit which if set at low speed which will allow for overheating on heater bank if set to run slow.

Did you look closely at the wiring diagram for the K1 contactor?

 

[Darkwood]

The only thing i see is if K2 is in and not K1 then you ill have 1ph to supply fan and signal out to relay but whatever is on 4t2 or 6t3 of K1 wont have supply well ... their will be a voltage present from the return of the motor.

This is what im on about .... i cant see what you are aiming at because i can't elliminate the countless issues i see with this set-up ...il be here all day for you to tell me something stupid i fear.

We have lack of full wiring plan to be able to elliminate all the other things that could be...ive probably already clocked it but as mentioned earlier the plans show no overload, the picture seems to lack one, the fault you had shouldn't have happened if system designed correctly I.e. air flow sensors, the thermal cutout in the heater should be its double redundency if other safety systems fail ...in a sense it a totally poor designed mess to start with and someone has added to it and made it slightly worse, i still see the SY cables taped off so sheath isn't earthed you say it is so how? Its got normal low voltage running through them so should be earthed.

 

[FrankUK]

If you look at the wiring diagram, you can see that there is a link from K1 to K2 on each phase and then, more importantly, there is U1, V1 and W1 wires feeding the fan motor, from terminals T1 T2 T3.

If you look at the photo's, you can see that the U1 wire (brown) has been disconnected from terminal T1 and used as the trigger input to the third party relay, leaving the fan motor operating on 2 phases. (grey and black wires)

The phase for the relay coil (A1 terminal) has then been taken from the T1 terminal of the K1 contactor.

Smart bit of wiring resulting in the fan motor running slower than expected then stopping due to overheating while the heater was on full fire. Without fan overrun being available to dissipate the residual heat, the High Limit stat has operated.

Hopefully, some of the guys on here that don't normally get to work on systems like this will learn something from this information.

 

[benji]

ok but got to ask where are the overloads

 

[FrankUK]

ok but got to ask where are the overloads

The motors do not have o/l's fitted but have internal thermal protection wired into the control circuit.

552.1.2 - the requirement (for o/l) does not apply to a motor incorporated in an item of current using equipment complying as a whole with an appropriate British Standard

 

[benji]

so the thermal protection are the 2 symbols shown on each motor wired in series

 

[Darkwood]

I did point out i couldn't see the wiring to the motor, i can see the loop to K2 contactor as per drawing and the brn tap off for the relay, the grey wire double up on the 2nd output of K1 i said i wasn't sure what that was for .... the picture wasn't clear enough to work out you issue as we cant follow wiring by sight and the cables are not number coded correctly....... i would be supprised if anyone could pull that from the info supplied but given the up hill struggle i guess i was as close as i could be given the info supplied......

Im aware that there are thermal cutouts in the motors but i still believe this system would benefit greatly from contactor overloads with thermal and magnetic trips, in any control system i only wire the thermal trips as a redundency in case of failure of other overload monitors, judging by the very basic lack of organisation, clear design flaws etc i can't believe it can comply to the appropriate BS standards...... although we are missing part of the diagram the thermal trips will probably reset automatically, is there any thermal monitor relays to hold supply out instead of allowing a reset button to be pressed on the operator controls thus putting the motor under repeated stress which can reduce its life if not destroy the windings.

 

[FrankUK]

so the thermal protection are the 2 symbols shown on each motor wired in series

Yes that's correct

 

[FrankUK]

I did point out i couldn't see the wiring to the motor, i can see the loop to K2 contactor as per drawing and the brn tap off for the relay, the grey wire double up on the 2nd output of K1 i said i wasn't sure what that was for .... the picture wasn't clear enough to work out you issue as we cant follow wiring by sight and the cables are not number coded correctly....... i would be supprised if anyone could pull that from the info supplied but given the up hill struggle i guess i was as close as i could be given the info supplied......

Im aware that there are thermal cutouts in the motors but i still believe this system would benefit greatly from contactor overloads with thermal and magnetic trips, in any control system i only wire the thermal trips as a redundency in case of failure of other overload monitors, judging by the very basic lack of organisation, clear design flaws etc i can't believe it can comply to the appropriate BS standards...... although we are missing part of the diagram the thermal trips will probably reset automatically, is there any thermal monitor relays to hold supply out instead of allowing a reset button to be pressed on the operator controls thus putting the motor under repeated stress which can reduce its life if not destroy the windings.

Yes, you were on the right track. If you look closely, you can see the U1 marking on the brown wire but it is not connected to the contactor K1, as per the wiring diagram.

The unit is a packaged heat recovery AHU complete with it's own controller and remote operator panel/keypad.

The fan trip and heater high temp trips are Class A faults and stop the unit immediately needing a user intervention to reset.

The kit is manufactured in Denmark and has CE marking, so adding additional overloads etc is something for the factory to include, if they feel they are necessary.

Bear in mind that I don't build or wire these units, only commission them or trouble shoot them. The third party additions were not in place when I commissioned this unit before Christmas.

As the orange relay is only switching the live feed into the third party fan controllers, a simple DPS across the AHU would have been a better option.