Two shower priority units in series

Crazyhorse99

Hello,

I'm looking for some advice from people in the know. We've got two electric showers in our house and we've a priority unit which only allows one shower to operate at once.

We are now hoping to have a 32A electric vehicle charger installed. Standard practice when installing EV chargers in houses with an electric shower (as far as I can tell) is to install a priority unit between the charger and the shower so only one could be used at a time (giving priority to the shower).

The company I've spoken to re installing the charger haven't come across a case like ours where we already have two electric showers. I had assumed that you could have two priority units in series - i.e. the supply from the main board coming into the new priority unit, with one output going to the EV charger and the other (the priority) as the input for the existing priority unit, which supplies the two showers.

The net result would be only one shower or the charger could operate at any one time, and priority would be given to the showers as it is now.

Has anyone any thoughts on this, specifically whether is would fall within RECI regs?

Any help much appreciated. Cheers.

Bruthal

It can be done as you have described with the new priority unit supplying the charger as secondary, and the second priority unit as primary.

Sleeper12

You can also get priority units made for more than two appliances. I've seen them used for three & even four electric showers. They get very expensive the more you want in them.

2011

The suggestion made in the OP aligns with the regulations as far as I am concerned.

Sleeper12 wrote: »

You can also get priority units made for more than two appliances.

I have never seen this, but it sounds like a better solution to me.

Sleeper12

2011 wrote:

I have never seen this, but it sounds like a better solution to me.

You have to order them as they are made to order. Regular priority is around 120. A triple is over 200. They aren't cheap.

Bruthal

2011 wrote: »

I have never seen this, but it sounds like a better solution to me.

It is, it just depends on whether the op wants to discard the existing one, and buy the expensive 3 way one. Or buy a second unit and add it in. Or buy a current sensing relay and contactor.

Crazyhorse99

Thanks all. Glad to hear it can be done. Re the three way switch, I've seen these on wholesaler websites and as far as I can tell (I'm no electrician), they only come in non-priority versions - i.e. which ever is on first has the power locked to it until it turns off. I'd rather not have a situation where the showers are locked out while the car is charging, I want the showers to have priority.
The company I've been in touch with were unsure how to proceed and whether the two priority units in series would be compliant with regs. He spoke to RECI and came back to me saying it couldn't be done, when pressed for a reason the answer was "it just wouldn't be right". He said the only way we could have a car charger installed would be to contact the ESB and have our fuse upgraded to 100A.

I'm very reluctant to disregard a pro's advice but based on what you guys have said, what I've read elsewhere, and a chat with another electrician, it sounds like it will actually work - and that there are a couple of other simple solutions too.

Thanks again.

Sleeper12

Crazyhorse99 wrote: »

Thanks all. Glad to hear it can be done. Re the three way switch, I've seen these on wholesaler websites and as far as I can tell (I'm no electrician), they only come in non-priority versions - i.e. which ever is on first has the power locked to it until it turns off. I'd rather not have a situation where the showers are locked out while the car is charging, I want the showers to have priority.
The company I've been in touch with were unsure how to proceed and whether the two priority units in series would be compliant with regs. He spoke to RECI and came back to me saying it couldn't be done, when pressed for a reason the answer was "it just wouldn't be right". He said the only way we could have a car charger installed would be to contact the ESB and have our fuse upgraded to 100A.

I'm very reluctant to disregard a pro's advice but based on what you guys have said, what I've read elsewhere, and a chat with another electrician, it sounds like it will actually work - and that there are a couple of other simple solutions too.

Thanks again.

Your electrician can order them in his wholesalers. As I say they are made to order so it takes a few days.

2011

Crazyhorse99 wrote: »

I'm very reluctant to disregard a pro's advice but based on what you guys have said, what I've read elsewhere, and a chat with another electrician, it sounds like it will actually work - and that there are a couple of other simple solutions too.

I understand your reluctance, but I can assure you that this can be done in a compliant and safe manner. For example, it would be possible use a 3 position selector switch that would ensure that only one of three suitably rated contractors could supply a shower or the charger at a time. To explain:

Switch in position #1: Contactor #1 energized so that it supplies power to shower #1 (the other 2 contactors are de-energized, therefore disconnected)

Switch in position #2: Contactor #2 energized so that it supplies supplies power to shower #2 (the other 2 contactors are de-energized, therefore disconnected)

Switch in position #3: Contactor #3 energized so that it supplies supplies power to the car charging unit (the other 2 contactors are de-energized, therefore disconnected)

As the selector switch can only be in one position at a time only one contactor can supply a load at any one time. So what safeguards do we have? In theory a faulty contractor could "stick" in the energized position. If this were to occur an "electrical interlock" could be used to ensure that no other contactor could energize until this fault is resolved. Secondly, even if this interlock were to fail the circuit design would ensure that a common MCB supplies all 3 contactors. This means that the MCB would operate (trip) if overloaded thus protecting the circuit conductors from an overload condition.

He spoke to RECI and came back to me saying it couldn't be done, when pressed for a reason the answer was "it just wouldn't be right".

I'm sure that I don't need to tell you that "it just wouldn't be right" is not a reason. This tells it's own story.

There are other solutions, such as using current sensing relays, the device suggested by Sleeper12 and even an app on your phone. All can be done in a safe and compliant manner, it may just be outside the scope of what some otherwise competent electricians deliver.

17larsson

The electric charger should have priority over the shower. We came across this before and the manufacturer of the charger said it could damage the internal electronics if it was regularly shutdown during charging.

Maybe contact the manufacturer of yours and see what they say

2011

17larsson wrote: »

The electric charger should have priority over the shower. We came across this before and the manufacturer of the charger said it could damage the internal electronics if it was regularly shutdown during charging.

I’m sure a 5 or 10 minute shower wouldn’t be an issue.
You could have the car charging all night, would you seriously allow this to stop you from washing??

DublinDilbert

It would be nice if the chargers were some what smart, they are expensive enough pieces of kit. If the charger could sense the incoming power to the house, it could then change the pilot signal to the charger in the vehicle to load shed. It could also be programmed to work with PV during the day time, if your exporting power your not being paid get the vehicle to take it, if connected.

17larsson

2011 wrote: »

I’m sure a 5 or 10 minute shower wouldn’t be an issue.
You could have the car charging all night, would you seriously allow this to stop you from washing??

It's the sudden cutting of power during charge that is the issue, not the length of time it is off for

2011

17larsson wrote: »

It's the sudden cutting of power during charge that is the issue, not the length of time it is off for

I doubt that.
What happens if there is a power cut?
What happens when the car is unplugged?

17larsson

2011 wrote: »

I doubt that.
What happens if there is a power cut?
What happens when the car is unplugged?

I'm talking about the charger not the car incase you're getting confused.

They told me if it was regularly shut down during charging it could cause problems with the electronics in the charger. When the car is unplugged power is still connected to the charger so no problem there obviously.

I don't know anything about the electronics inside it so I'm just saying what they told me. I'll find the email and post it here

listermint

17larsson wrote: »

I'm talking about the charger not the car incase you're getting confused.

They told me if it was regularly shut down during charging it could cause problems with the electronics in the charger. When the car is unplugged power is still connected to the charger so no problem there obviously.

I don't know anything about the electronics inside it so I'm just saying what they told me. I'll find the email and post it here

If what this random customer service rep said was true no ev chargers would work what so ever with a priority switch.

And we would have a large thread in boards about all the failed Ev chargers


Food for your consumtion..

2011

17larsson wrote: »

I'm talking about the charger not the car incase you're getting confused.

Thanks for the clarification, I was confused

I agree with listermint's post above.

If you are correct it should not be too difficult to link to a data sheet stating this can be an issue.

Tails142

I don't know the reason but just at a guess there might be cooling fans in the charger unit to keep the electronics below a certain temp, and if power shuts off instantly this air cooling stops and temps may spike up for a short while. I've never seen one of these units so it's just a guess

Bruthal

I doubt there is any problem having an electric vehicle charger in a priority switch setup. If there is, no one will be wanting lifts off electric vehicle owners.

2011

Tails142 wrote: »

I don't know the reason but just at a guess there might be cooling fans in the charger unit to keep the electronics below a certain temp, and if power shuts off instantly this air cooling stops and temps may spike up for a short while.

Apart from the points raised in the 2 posts just before yours heat is a function of current. Once the unit is disconnected the charging current ceases to flow, therefore it lo longer generates heat. I am not familiar with these units, however I am quite confident that they contain large heat sinks which will continue to dissipate heat once the supply is disconnected.

I would also think that the manufacturer of these units would have to consider that the supply may be disconnected at anytime for a variety of reasons, therefore this would have to be reflected in the design to ensure a robust unit.

No doubt someone will post a link to a manufacture's data sheet or manual showing otherwise if I am incorrect. Here is a link to the BMW Wallbox Pro installation manual. I had a quick scan through this and nothing caught my eye to suggest that this could be an issue.

Crazyhorse99

Thanks for the further replies. I’ve been in touch with Rolec (charger manufacturer) re disconnecting mid charge. He wasn’t too worried from the point of view of the charger, but did say that the vehicle batteries fare out better if charged continuously and not interrupted.
In reality the number of times a shower would interrupt charging would be rare. The car would be charged at night on night rate electricity, day time chargignwould be minimal to reduce cost.
Just need to find another installer now. I’m tempted to just find a local electrician and ask them what they think, as opposed to looking for a specialist installer.

Bruthal

Crazyhorse99 wrote: »

Thanks for the further replies. I’ve been in touch with Rolec (charger manufacturer) re disconnecting mid charge. He wasn’t too worried from the point of view of the charger, but did say that the vehicle batteries fare out better if charged continuously and not interrupted.
In reality the number of times a shower would interrupt charging would be rare. The car would be charged at night on night rate electricity, day time chargignwould be minimal to reduce cost.
Just need to find another installer now. I’m tempted to just find a local electrician and ask them what they think, as opposed to looking for a specialist installer.

Someone with any technical ability can easily set that up with your existing priority unit plus a second one, or add in a current sensor and n/c contactor on the charger supply. Charger should be supplied by same breaker as the showers. Current sensor goes on the supply link to the 2 showers so it doesn't sense the current to the charger.

I never used 3 way priority/non priority units but they might be fully non priority. It has to be a priority setup in this case, rather than first come-first serve.

Crazyhorse99

Bruthal wrote: »

I never used 3 way priority/non priority units but they might be fully non priority. It has to be a priority setup in this case, rather than first come-first serve.

Funnily enough I've been thinking about this and I reckon the 3-way non-priority could work. If the car's charging and the shower won't come on, you just go into the vehicle manufacturer app and stop the charge remotely. It would have the added bonus that neither shower would have priority over the other. I.e. whoever's in the shower first won't be interrupted!

Bruthal

Crazyhorse99 wrote: »

Funnily enough I've been thinking about this and I reckon the 3-way non-priority could work. If the car's charging and the shower won't come on, you just go into the vehicle manufacturer app and stop the charge remotely. It would have the added bonus that neither shower would have priority over the other. I.e. whoever's in the shower first won't be interrupted!

Yes that would work.

On the shower priority just purely as a matter of interest, a non priority unit can be used for the 2 showers, and a priority unit for charger and shower non priority unit. So showers would be first come first serve, but either one would have priority over the charger.

As said, just a matter of interest there for anyone it might be of interest to.

pauldavis123

Is it possible to upgrade the kVA coming into your house to allow you to shower and charge or to run both showers?

Tuco88

A 3phase supply... But its very expensive to install.

2011

Tuco88 wrote: »

A 3phase supply... But its very expensive to install.

I would rather replace the showers for a non-instantaneous type. A better shower and all of these issues simply disappear.

punisher5112

I had this in my dad's house and he got solar tubes in that heat the water.

So now only one shower but I still have the unit fitted as it would be ideal if a ev were to be housed there in the future.

Crazyhorse99

We’re currently on an 8kVA supply. The ESB are upgrading that to 12kVA free of charge. The tails at our house are adequate so it’s essentially just a paper work exercise (I’m told).
We can go up to 16kVA if we want, but there’s an €1100 charge for that. Thinking down the road, we’ll probably do that when we change our second car for an electric one - we may need two chargers.
By then I’ll hopefully have replaced the boiler and done away with electric showers all together.

2011

Crazyhorse99 wrote: »

We’re currently on an 8kVA supply. The ESB are upgrading that to 12kVA free of charge. The tails at our house are adequate so it’s essentially just a paper work exercise (I’m told).

The house will need to be rectified which will incur a cost, in addition the distribution board main fuse and fuse holder will need to be upgraded.

We can go up to 16kVA if we want, but there’s an €1100 charge for that. Thinking down the road, we’ll probably do that when we change our second car for an electric one - we may need two chargers.
By then I’ll hopefully have replaced the boiler and done away with electric showers all together.

Changing the showers for non-instantaneous type has the following advantages:
1) Better showers (higher volume of hot water at greater pressure)
2) Cheaper showers (running cost as heating water electrically is expensive)
3) No need for priority units required even when you have a 2nd electric car (depending on other electric loads) which are expensive and have been known to fail.
4) No need for an "enhanced single phase supply" (16 kVA) which may incur a more expensive standing charge (someone else can advise on this).

pauldavis123

Does three phase have bands like the 8, 12 and 16 kVA ones of single phase?

I can't find any info on domestic three phase, any pointers?