Is this Bad Practice

[Dimspark]

Guys
Need some advice please. I was asked last week to investigate a burning smell in a toilet turned out it was an extract fan one of 2
The setup is a twin set of fans lead and standby the only time the standby fan comes on is if the lead fan fails the standby fan simply overheated as it had seized due to it never being used there is no facility to change the duty of the fans .
I am thinking about installing contactors with thermal overload and a timer to change over the fan duty on a weekly basis my problem is there is no space available to install an enclosure on the fan housing there is space inside the fan housing to install the new controls on a din rail the fan enclosure is ceiling mounted would it be bad practice to use the fan housing as an enclosure . .
Access to the fans is by removing a cover which is secured by machine screws.
Thanks Dimspark

 

[littlespark]

I guess this isn’t a domestic WC…. So commercial?

Would there be a problem if both fans just ran together, without any duty cycle changeover?

 

[snowhead]

Presumably if one fan is burnt out after being called for on failure of the other then the whole unit is being replaced, so can have a unit that does change over, I'm sure nowaday they all would.

And I'm sure all the twin commercial toilet fans I dealt with over the years used to swop fans every time the unit was powered, is this one running 24 / 7?
It was rare to ever get a like for like replacement or even spares as most went obsolete, especially when the E.U brought in energy saving directives on motors.

 

[Avo Mk8]

Is the space "inside the fan housing" that you are contemplating using for the control circuit actually in the airflow that the fan is moving, or is it a separate enclosure isolated from the airflow?
The reason I ask is that controls must be suitable for the environment they are used in, and the air being moved out of the room may be moist /corrosive/ dusty and incompatible with the IP rating of naked components.

The other issue is that you would assume 'design responsibility' for the modified units, since the original design approval of the product has been superseded by your modifications, so if anything goes bad in the future you could be in the firing line as the responsible party. Depending on your contractual relationship with the business you are helping, and your insurance, this may or may not be an issue!