# Wiring/symbol help...

#### cpu888

Joined Sep 17, 2021
12
How many amps would this relay/contactor external switch draw for it to be adequately safe in comparison to a full 2kw heater?

So if I was to play it safe and create an external switching device, what would that be. I have no idea. I've seen information that the Salus Reciever would go to a relay and then to a contactor then to the heater. So I need a relay or contactor or both? Are there any neat already housed affordable creations of this external switching mechanism?

Last edited:

#### ericgibbs

Joined Jan 29, 2010
14,157
How many amps would this relay/contactor external switch draw for it to be adequately safe in comparison to a full 2kw heater?
If you mean the Rated current of the Contacts
Exactly the same as the contacts in the Thermostat ie: 230Vac 16Amps

Joined Jul 18, 2013
23,913
Relay style Zettler AZ2280-1C-240V

#### cpu888

Joined Sep 17, 2021
12
If you mean the Rated current of the Contacts
Exactly the same as the contacts in the Thermostat ie: 230Vac 16Amps
what the coil of the external relay would draw

Joined Jul 18, 2013
23,913
1Amp, give or take.....

#### MisterBill2

Joined Jan 23, 2018
9,802
If you mean the Rated current of the Contacts
Exactly the same as the contacts in the Thermostat ie: 230Vac 16Amps
THE QUESTION WAS PERFECTLY CLEAR!!! The TS was asking about the relay coil current, NOT the contacts rating. And the answer is that it depends on both the size of the relay and the coil voltage. For a 230 volt coil the current would certainly be less than half an amp, probably closer to a tenth of an amp.

#### ericgibbs

Joined Jan 29, 2010
14,157
Hi 2,
In my opinion this TS is being given very poor advice, regarding the need of a second relay.

If you take to time to check the Thermo units documentation, you can clearly see that it is well established Company with a good product range.

If it used 'flimsy' relays in its products it would soon be out of business.

With regard to this comment; THE QUESTION WAS PERFECTLY CLEAR!!!
As a double check I asked the TS, not You: If you mean the Rated current of the Contacts.

So many times the TS's are not technically savvy about electrical terms, so I often ask for confirmation.

Anytime I want to ask, any TS a question, I will continue to do so without having to get your consent, OK.?

E

#### MisterBill2

Joined Jan 23, 2018
9,802
The reason that I commented on an external relay is that the question was asked.
The possible reason for using one would be in the wiring to the thermostat. If it was inconvenient to run the heavier conductors to the receiver location then a relay may be a benefit, even if it meant using an external transformer to power a lower voltage relay. Sometimes that is a consideration, sometimes it is not.

#### cpu888

Joined Sep 17, 2021
12
Prehaps I should just leave the thing alone?

#### ericgibbs

Joined Jan 29, 2010
14,157
hi cpu.
I have emailed the Salus sales depot, a few days ago, so far no reply to my query.

E

Copy:
Eric Gibbs
Sun, 19 Sept at 09:50

hi,
I have a colleague who has a RT310RF unit, he asks, will it be suitable for use with a 2KWatt, 230Vac Heater.[ UK ]
I see that the Relay contacts are Rated for 230Vac at 16Amps maximum.
I have assured him that the Heater will only draw ~9Amps and the relay will be OK, please confirm.

Regards
Eric Gibbs C Eng; M.I.E.T.

Last edited:

#### cpu888

Joined Sep 17, 2021
12

"You need a 230vac coil relay who's contacts can handle the load of the heater. 2Kw?
The thermostat switches the coil, as shown."

"I would hesitate to switch 2kw with the internal relay, most room temperature thermostats i am familiar with use the internal contacts to pick up an external relay when operating the typical furnace fan/input, etc."

"The symbols appear to be either a fan or a solid state circuit.
Or a low voltage input to a electric furnace"

"Whatever you are switching at 2kw, personally i would use an external relay to switch it, rather than the thermostat take the brunt of the load, and more  to replace."

"Generally an ordinary house HVAC thermostat switches the gas valve on for gas heating, and starts the heating element start sequence for the electric furnace.
Or the compressor relay for cooling."

"Yes you most likely can control it directly But,
You most likely have one of those small PCT relays inside that unit, and although most claim fairly high current rating, they can be a source of failure in many appliances, also Is the PCT the relay is soldered to capable of 16A?
Personally for the cost of an external relay, i would prefer to play it safe."

"Relay style Zettler AZ2280-1C-240V"

"1Amp, give or take....."

"30amp form A contacts.
There is always the possibility of poor engineering, you would need to open and inspect to be sure."

-----------------------

Hi, MaxHeadRoom, I seem to be having a communication error.

Are you advising me that it would cost me alot to keep replacing the unit if it failed?
or
Are you advising me that this is a danger of a 'fire' if it failed?

You've said: "You need a 230vac coil relay" "I would hesitate to switch 2kw with the internal relay" "personally i would use an external relay to switch it, rather than the thermostat take the brunt of the load, and more  to replace." "Yes you most likely can control it directly But, You most likely have one of those small PCT relays inside that unit, and although most claim fairly high current rating, they can be a source of failure in many appliances, also Is the PCT the relay is soldered to capable of 16A?
Personally for the cost of an external relay, i would prefer to play it safe." "There is always the possibility of poor engineering, you would need to open and inspect to be sure."

Again, I seem to be having a communication error.

I am not worried about the cost of the unit to replace if it fails. I am worried about it setting fire and burning me and everything I own if it fails.

Why are you advising me to be worried if it fails and I should play it "safe"?

What do you mean by "they can be a source of failure in many appliances" and "i would prefer to play it safe."?

**What would happen if it failed? What would physically happen?

So, again my first question at the start of this post...
Are you advising me that it would cost me alot to keep replacing the unit if it failed?
or
Are you advising me that this is a danger of a 'fire' if it failed?

I hope you can understand my communication error and can comment on this post as it seems to be a confusion for me between fire or money.

Replies appreciated.
Thanks

Last edited:

#### Yaakov

Joined Jan 27, 2019
3,739
Of course @MaxHeadRoom can speak for himseof and I expect he will but as someone following from the sidelines my impression is the intends to warn you of both things: potential safety hazards and unnecessarily high cost of repair.

The former would comprise:

1) Misleading rating on the relay, either on account of overrating by the manufacturer of the part or because it has been placed on a board that might not match the relay‘s ratings, causing the entire system to be derated.

2) Failure modes of the relay possibly causing unexpected operation. Failsafe is always the goal for control systems but if the relay were to fail by welding its contacts on, it would keep the heater running when the thermostat is no longer calling for heat. This could be dangerous if not detected.

The latter is based on the idea that if the relay in the thermostat dies (which small relays like that do more than larger ones when being used at high voltages and currents) it might require replacing the entire thermostat instead of an inexpensive external relay which is, in any case, less prone to the sorts of failures miniature versions are.

Just how much I agree with this advice isn’t clear to me, but I do trust Max and so I wouldn’t dismiss it lightly. Certainly worth considering.

Joined Jul 18, 2013
23,913
Hi, MaxHeadRoom, I seem to be having a communication error.
I hope you can understand my communication error and can comment on this post as it seems to be a confusion for me between fire or money.
Mainly suggested advice on whether to risk the durability of the thermostat, I have seen and repaired a few appliances that switch these kind of loads with where either the internal relay fails or the PCT is damaged due to insufficient Cross sectional area.
The unit is evidentally rated for your intended load, it is just a question of whether you wish to risk a potential failure at some later date.
I simply suggested a course of action I might consider to prevent a loss of a device that may incur un-neccessary expense.

.

#### ElectricSpidey

Joined Dec 2, 2017
1,962
I love the logic on this thread...

If safety is the main concern, then have an amateur modify the system...yea that makes sense.

I can think of more than a few ways that could go wrong.

#### cpu888

Joined Sep 17, 2021
12
Mainly suggested advice on whether to risk the durability of the thermostat, I have seen and repaired a few appliances that switch these kind of loads with where either the internal relay fails or the PCT is damaged due to insufficient Cross sectional area.
The unit is evidentally rated for your intended load, it is just a question of whether you wish to risk a potential failure at some later date.
I simply suggested a course of action I might consider to prevent a loss of a device that may incur un-neccessary expense.

.
Hi. Thanks. I think I can understand that now. As a usual plugged equipment buyer/user, reading some of your replys on this post/thread has somehow lead me to try and understand if the company would sell a product that would burn a house down if the contacts/PCT so called 'fails'.

So, out of interest & understanding....

Question 1
If the 'internal relay' so called 'failed' ... what exactly would happen?

Question 2
If the PCT so called 'failed' ... what exactly would happen?

Questin 3
If 'both' the 'internal relay & PCT' so called 'failed' ... what exactly would happen?

Last edited:

#### ElectricSpidey

Joined Dec 2, 2017
1,962
If contacts fail "open" nothing happens.
If contacts fail closed then the power remains on to the heating unit, where hopefully the proper overheat devices are installed.
If the contacts fail by developing a high resistance then they could overheat.

Last edited:

Joined Jul 18, 2013
23,913
So, out of interest & understanding....

Question 1
If the 'internal relay' so called 'failed' ... what exactly would happen?

Question 2
If the PCT so called 'failed' ... what exactly would happen?

Questin 3
If 'both' the 'internal relay & PCT' so called 'failed' ... what exactly would happen?
In all cases above, the unit will no longer have any control of the appliance etc.
In the cases I have experienced with appliances switching this kind of load, either the relay itself goes open, or the PCT to one of the terminals open circuits,

#### cpu888

Joined Sep 17, 2021
12
In all cases above, the unit will no longer have any control of the appliance etc.
In the cases I have experienced with appliances switching this kind of load, either the relay itself goes open, or the PCT to one of the terminals open circuits,
Thanks for the information. I find that very useful.

Well, in terms of you saying "i would prefer to play it safe"... this is not related to any fire hazzard if I use it as it is?
It should be safe in terms of fire hazzard to run it as it is but it may just need replacing or fixing?

If you can understand my confusion & concern