3phase to single new pump set

[Peakyblinder89]

Hi all, been a member for a while but this is my first post so hoping you can help. Been asked to install new twin set of pumps. Pictures attached of old pump (3 phase) and new pump (single phase) and the contactors And overload for the pumps . Best and easiest way to change to single phase for the new twin set as the old pump has no neutral at the isolator? Thanks much appreciated

 

[James]

Quite a lot of work to change over that lot.
Are you responsible for building the control panel as well?
Also, have you noticed that the new pump is not as powerful as the old one?
1150w vs 760w

 

[Peakyblinder89]

Hi James , yes it got dropped on me last thing yesterday ‘could I come over and connect the next pump’ you no that old chestnut. Yes the mechanical guys are aware the new pump is 760W, apparently Grunfoss don’t do 3phase replacements they are all single phase now. Yes I’m responsible for the control side of things . Thanks for your reply

 

[James]

I would be making a new control panel, correct sized overloads for single phase motors.
If you can’t get a neutral to that point, then your only option is an isolating transformer to go from 400v across phases to 230v from ground to new Live.

 

[Darkwood]

What is the chances of getting a N to the panel, the controls can be adapted quite easily using existing and at most swapping out the O/L's ... of course you will have to draft up a new wiring plan to show either the alteration or to replace the existing plan.

PS - the pump sizing and power rating is down to the plumber to spec', just adapt your panel to what pump he chooses, if the pumps are not correctly rated then any further costs to yourself can be invoiced for.

 

[Peakyblinder89]

dark wood I was thinking using L1 as my L and using L2 as my N cable... obviously connecting to the N on the contactor. What’s your best way of going about it? Yes I will draw up everything I do and leave on site in the panel . Yes the pump set is down to the mechanical guys he only found it it was single phase when the new pump set arrived on site

 

[snowhead]

The design of pumps for the last 10 years or so have moved on considerably, mainly due to E.U energy saving legislation, the same reason that domestic pumps have changed from the old 3 speed pumps.

Like the O.P, pumps that were 3ph are now single with reduced power consumption but still the same output.

There's a neutral in the panel but just not at the pump isolator(s)?
If so, use one of the redundant phase cables as Neutral.
Good practice would be to change both the contactor and the overload but if the existing overload will cover the new pump rating you could use that.

If you're changing the contactor check the coil voltage, quite possibly will be 24v ac but could be any voltage, also make sure you've got enough aux contacts on the new one.

 

[James]

You need to be careful, I did think about using one of the spare L conductors as a N but you may well have a 3 phase blower on the boiler so might not be an option.
Also you might not get a suitable overload for the contactor since telemech are now Schneider and they are old range.
Not all overloads are happy with a single phase load as they see it as a lost phase. Check the spec of overloads carefully.

I have done many similar type conversions and wished when I was half way through that I had built a new panel instead of trying to adapt what was there for various reasons.

The cost of the parts is often offset by the ease of installation and commisining

 

[Timbo]

@James: the pump won't have anything to do with the boiler, that will be a separate contactor.
I used to loop the live through 2 contacts to keep the overload happy. Out of the first and back up to the second, out of the second to the motor.

 

[James]

@James: the pump won't have anything to do with the boiler, that will be a separate contactor.
I used to loop the live through 2 contacts to keep the overload happy. Out of the first and back up to the second, out of the second to the motor.

I understand that, often the pumps are fed from the same supply as the boiler. If the boiler requires 3 phase for the blower, you are stuffed and can’t use a spare phase cable as a neutral because there are no spare phase cables.

 

[Timbo]

These are fed directly from the panel, each from its own contactor.
There will be a fused supply for each item.

 

[Lucien Nunes]

I think there's confusion about whether the supply to just the pump needs one line repurposed as the neutral, or whether that applies to the whole panel. As I read it, it's only the run from contactor to pump that is missing a black cable. There's a neutral in the panel that could be sent to the pump if a cable is provided / repurposed for it.

The O/Ls on S1 & S2 don't go up to the new pump's 3.4A FLC. Whether that's a problem depends on whether the correct adjustment is within the current O/L rating.

 

[John Brown]

I have a video about single phase into three phase, but I can't post the video on it. If you need it, maybe I can upload it on facebook.