Control relay spec.

[dogleg43]

Would someone be able to tell me what this means on a specification for relay contacts: "......10 amp make, 1.5 amp break."

Is this the same thing as saying the contacts need to be rated for a 10 amp continuous load?

The rest of the relay spec seems clear, coils may be either 120VAC or 24VDC, din rail mount, etc. etc.
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We're trying to meet a boiler plate specification written by consultants and the RFI process isn't always helpful. Usually when asking what do they mean by xxxxx, the response is "provide per the specification."

 

[cornbread]

I think for resistive load the make and break are the same, for inductive load they are less. So I think what you have is a 10 amp contact for a resistive load and 1.5 amp for a inductive load.

 

[bernie_carlton]

First let's have a discussion about a phenomenon called an 'arc'. An arc is an electrical pathway formed by ionized air between two normal conductors, the spark when you touch a doorknob for example.

Contacts, which already have voltage applied, at some very close point will establish an arc between them - the distance based on the voltage. As the contacts are already closing this typically has little effect.

As contacts begin to open the voltage will ionize the air between the slightly open contacts and current will continue to flow. It takes a certain amount of voltage and current to sustain an arc of a given length. As the contacts open further the voltage and available current cannot sustain the arc and it dies as the contacts reach their full separation.

The lower number is threshold of the current at the rated voltage which cannot sustain an arc across the separation of the contacts.

Thus, if this relay were to be used to pass a current below the 'make' rating but higher than the 'break' rating some other device must actually break the circuit before this contact opens.

And indeed as cornbread notes inductive circuits are, upon 'break', more likely to 'kick back' with a voltage and current capacity far above that which was being passed to the inductive load. Thus the need for arc suppression circuitry across the relay contacts.

 

[Geospark]

...I think what you have is a 10 amp contact for a resistive load and 1.5 amp for a inductive load.

Not to say the continuous resistive rating for this relay is not 10 amps, but the 10 amp make rating is only referring to the make rating of an Inductive load, so we cannot really assume this to be a continuous rating for a resistive load.

A Resistive load will indeed have the same rating for make, break and continuous amps, while an Inductive load will have a different rating for make, break and continuous amps.

...Is this the same thing as saying the contacts need to be rated for a 10 amp continuous load?...

No...

Example: A relay with a contact rating of 40 amps at 240VAC Resistive has a make, break and continuous rating of 40 amps each. The same relay contact, when switching an Inductive circuit, will have a different amperage for each of its make, break and continuous ratings. It will have a continuous rating of only 10 amps for an Inductive load at 240VAC; the MAKE rating at 240VAC will be 30 amps, however, the BREAK rating is only 3 amps at 240VAC.

So, if you are switching an Inductive load, the 10 amps make rating you have read does not necessarily imply that it is 10 amps for a continuous Inductive load. If the make is only 10 amps, then the continuous rating for an Inductive load might be less, more like 8 amps continuous, but not always. It depends a lot on which voltage you are working at. At 120VAC, an Inductive load on a contact could have a make rating of 60 amps, and a continuous rating of 10 amps. However, if we go up to 600VAC, then the make rating could drop to say 12 amps, and the continuous to around 10 amps. So at higher voltages, the difference between the make and continuous ratings is far less than at lower voltages.

The spec you've quoted above only matters if you are switching an Inductive load. If resistive, you need to find the continuous rating for a resistive load in the specs; this will also be its make and break rating.

More specific to bernie's info...

Arcing with inductive loads such as motors; when a circuit is applied to a winding, that winding creates a magnetic field and induction occurs. When the circuit is broken the magnetic field collapses, and this generates a voltage spike and creates an arc at the breaking point of the circuit's path. i.e. the contact. This is why, for inductive loads, the contact ratings differ for make, break and continuous compared to resistive loads which do not suffer the same effects. Both types of loads, of course, have their own drawbacks and suppression methods to overcome them.

Regards,
George

 

[nehpets]

It maybe due to contact separation distances, the relay will have no problem closing on a 10 amp load, but due to contact separation distance being quite small, the current it can break is restricted to 1.5 amps because of arc flash over at higher currents.

Steve

 

[Lancie1]

Would someone be able to tell me what this means on a specification for relay contacts: "......10 amp make, 1.5 amp break."

Bacially, it means those relay contacts can handle up to 10 amps while closing, but only 1.5 amps while opening.

 

[dogleg43]

Bacially, it means those relay contacts can handle up to 10 amps while closing, but only 1.5 amps while opening.

Thanks Lancie. That Seems to make sense.

The consultants who write the specification rarely give a straightforward answer when they are asked what a statement means.

 

[jraef]

Thanks Lancie. That Seems to make sense.

The consultants who write the specification rarely give a straightforward answer when they are asked what a statement means.

Marketing departments are full of people who are not engineers, but are adept at obfuscation, especially of product deficiencies. From a manufacturer's standpoint, they should list the make, break and the continuous current ratings, but "continuous current" is a conditional concept, which makes the way you define it somewhat open to interpretation if not clearly stated. Those marketing types will often find ways of being less than fully open about things they perceive the buyers will not notice. So the person who wrote that spec is saying, in effect;

"I don't care what marketing spin you want to place on your continuous current ratings, what I am really after is that I want the contacts to handle at least 10 amps while closing, and at least 1.5 amps while opening"

 

[jdbrandt]

Would someone be able to tell me what this means on a specification for relay contacts: "......10 amp make, 1.5 amp break."

Is this the same thing as saying the contacts need to be rated for a 10 amp continuous load?

The rest of the relay spec seems clear, coils may be either 120VAC or 24VDC, din rail mount, etc. etc.
==================

We're trying to meet a boiler plate specification written by consultants and the RFI process isn't always helpful. Usually when asking what do they mean by xxxxx, the response is "provide per the specification."

Good Luck.
This is his own spec.(i.e. not one of the NEMA standards), and does not give enough information.
I.E. AT WHAT VOLTAGE

NEMA C150 -or- C300 -or- C600 would be 15/1.50 @120V, but only 7/5/0.75 @240V

 

[dogleg43]

Good Luck.
This is his own spec.(i.e. not one of the NEMA standards), and does not give enough information.
I.E. AT WHAT VOLTAGE

NEMA C150 -or- C300 -or- C600 would be 15/1.50 @120V, but only 7/5/0.75 @240V

The relay contacts I'm asking about will be switching small 120VAC or 24VDC loads such as motor starters, other relay coils, pilot lights.

 

[Lancie1]

The relay contacts I'm asking about will be switching small 120VAC or 24VDC loads such as motor starters, other relay coils, pilot lights.

The "break" or opening current for an inductive coil such as a motor starter coil, can easily go above 1.5 Amps at 120 volts. Get as much "break" capacity as you can.