Connecting secondary xfmr hots together? good/bad practice

[rco-afe]

We deal mainly with overhead material handling equipment, and find many applications where on a particular crane/hoist situation the designers have tied the secondary hot (x1) from several control transformers together. They remove the ground for the neutral side to avoid power issues;
the question is is this a good practice?

 

[qcroanoke]

We deal mainly with overhead material handling equipment, and find many applications where on a particular crane/hoist situation the designers have tied the secondary hot (x1) from several control transformers together. They remove the ground for the neutral side to avoid power issues;
the question is is this a good practice?

We used to do that on HVAC controls, tie all the secondary hot's and commons together for control power.
Worked fine until UL decided that the secondary was a separately derived system and made the HVAC mfgrs. ground the common of the xfmr. We used a 2 stage t'stat to control the 2 units and if you turned off 1 of the units and lowered the t'stat to where both units should run it would try to run the unit that was off through the control xfmr.
Needless to say xfmr didn't like that and didn't last long either....
The fix was to take ground of secondary loose. But it also voided UL listing.
To answer your question, no, it is not a good practice to remove the n/g bond of a control xfmr. Especially if it was there from the factory and the unit is UL listed.

 

[rco-afe]

We used to do that on HVAC controls, tie all the secondary hot's and commons together for control power.
Worked fine until UL decided that the secondary was a separately derived system and made the HVAC mfgrs. ground the common of the xfmr. We used a 2 stage t'stat to control the 2 units and if you turned off 1 of the units and lowered the t'stat to where both units should run it would try to run the unit that was off through the control xfmr.
Needless to say xfmr didn't like that and didn't last long either....
The fix was to take ground of secondary loose. But it also voided UL listing.
To answer your question, no, it is not a good practice to remove the n/g bond of a control xfmr. Especially if it was there from the factory and the unit is UL listed.

Thanks for the input, we have two parallel bridge crane runways and there are 4 separate bridges and hoists on each runway that have the ability to project the hoist into the other runways area. thus providing a possible collision. Each runway is feed from a different bus tap and disconnect. One sides elevation is higher so as to not colloid with the other bridge allowing the transport of material from runway to runway. They have it set up on a bus or power tract system that if one side sees by photoeye another bridge in its pass it will send a hot signal to the other runway indicating it is not clear for the other bridge to project. In short I have 4 xfmrs from 4 individual control boxes feed by one bus tap that could simultaneously seen a 120vac signal to 4 other control panels with 4 xfmrs feed from a different bus tap. they are not using a relay to isolate the circuit.

 

[jim dungar]

A control transformer has two terminals X1 and X2 - not 'hot and neutral'.

Many decades ago it was common in heavy industries like automotive and steel to ground (or common) the X1 terminal of control power transformers while fusing the X2 side.

 

[qcroanoke]

Also, welcome to the forum!
Hopefully others will post their thoughts on this.