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'[EE]: Understanding Terminal Block Ratings'
2002\09\02@152920 by

Hello,

I wish to purchase a two-screw terminal strip to wire in the leads of a motor.  Now, this motor will be running at 24V and will have a maximum continuous current draw of 40A.
My question is how to interprete the ratings for terminal blocks.  Specifically, the Molex terminal blocks I am looking at how ratings such as 10A @ 250V.  Are these absolute maximums?  That is, the current must be less than 10A and the voltage must be less than 250V.  What confuses me is why the amp rating is qualified with a given voltage.  How does it matter if I am putting 10A into the connector at 10V or 300V - the power dissipated in the connector is the same (I^2 * R).

Another question: Can anyone suggest a connector to use that can handle 40A?  I've been able to find a terminal block that can handle more than 25A.  What is commonly used as a connector for high current loads such as a motor?

Thanks,
Donovan

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In a message dated 09/02/2002 15:30:32 Eastern Daylight Time, dparksUVIC.CA
writes:

> Another question: Can anyone suggest a connector to use that can handle 40A?
>  I've been able to find a terminal block that can handle more than 25A.
> What is commonly used as a connector for high current loads such as a motor?
>

For Donovan

The usual practice is to use "contactors", which are nothing more than high
current relays.  They are available at Digikey at up to 100 amps.

Sid

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Current ratings hinge largely on how much heat the terminals and wire can
take, and how much power you are willing to lose.  At a higher voltage you
can afford to lose more voltage in the connector.  Most high power
connectors have a resistance rating in milli-ohms.  Use the milliohms to
calculate the losses and see if they are acceptable to you.  Note that if
the current is short term or intermittent you can probably bend the rules
quite a bit.

Doug Butler
Sherpa Engineering

> {Original Message removed}
At 03:49 PM 9/2/02 -0400, you wrote:

>For Donovan
>
>The usual practice is to use "contactors", which are nothing more than high
>current relays.  They are available at Digikey at up to 100 amps.

Connectors are different from contactors.. high current connectors are more
industrial products, look at twist-lock and similar connectors, for example.
There are waterproof, particularly rugged and other specialist types,
which don't typically show up in electronics distributor catalogs.

BTW, contactors are not quite the same as relays. Relays usually put the
current through a flexure (a wire or spring), a construction suitable for
low currents. Contactors typically have twice as many contacts per pole,
and bridge between two contacts with a moving shorting bar, a construction
that is more rugged on overload, and more suitable for high currents.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
speffinterlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com
9/11 United we Stand

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Go careful.
Terminal blocks are pretty notorious for long term failures with highish
current. The heat generated can increase the oxidation of the wire,
softening of the plastic and loosening of the clamp pressure which
increases the resistance, the heating and the problem.

If the usage is intermittant you may get  away with using a lower rated
connector but if the application is critical or the connection cannot be
easily monitored or the environment is hot to start with  then you may want
something better.

- Properly Crimped lugs and decent sized brass bolts & nuts for example.

One thing that can assist is to crimp the wire ends together into a ferrule
before inserting into the terminal block - we use these for MCB connections
up to about 120Amps.

An electrical supply shop should have terminal block type connectors for
the higher currents - just make sure they are done up real tight if you
decide to use them.

Richard P

Hello,

I wish to purchase a two-screw terminal strip to wire in the leads of a
motor.  Now, this motor will be running at 24V and will have a maximum
continuous current draw of 40A.

My question is how to interprete the ratings for terminal blocks.
Specifically, the Molex terminal blocks I am looking at how ratings such as
10A @ 250V.  Are these absolute maximums?  That is, the current must be
less than 10A and the voltage must be less than 250V.  What confuses me is
why the amp rating is qualified with a given voltage.  How does it matter
if I am putting 10A into the connector at 10V or 300V - the power
dissipated in the connector is the same (I^2 * R).

Another question: Can anyone suggest a connector to use that can handle
40A?  I've been able to find a terminal block that can handle more than
25A.  What is commonly used as a connector for high current loads such as a
motor?

Thanks,
Donovan

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"Can anyone suggest a connector to use that can handle 40A?  I've been able
to find a terminal block that can handle more than 25A.  What is commonly
used as a connector for high current loads such as a motor?"

There is a connector reffered to as a "Power-Pole" that is very popular in
modelling and Ham Radio that is very easy to find (not Radio Shack though)
in 15 and 20 AMP sizes. I am pretty sure they are available in larger sizes
as well.

John Ferrell
6241 Phillippi Rd
Julian NC 27283
Phone: (336)685-9606
Dixie Competition Products
NSRCA 479 AMA 4190  W8CCW
"My Competition is Not My Enemy"

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John Ferrell wrote:
>
> "Can anyone suggest a connector to use that can handle 40A?  I've been able
> to find a terminal block that can handle more than 25A.  What is commonly
> used as a connector for high current loads such as a motor?"
>
> There is a connector reffered to as a "Power-Pole" that is very popular in
> modelling and Ham Radio that is very easy to find (not Radio Shack though)
> in 15 and 20 AMP sizes. I am pretty sure they are available in larger sizes
> as well.

Hi John, the method I prefer is to use cheap
(and common) automotive plugs, line plug and
socket. They have a number of spade lugs and
matching sockets about 15A rated I think.
Parallel the connections for larger currents,
and that increases contact reliability over
that of single connections too.

I would stay away from terminal blocks as a form
of high current connector. :o)
-Roman

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John Ferrell wrote:
>>
>> "Can anyone suggest a connector to use that can handle 40A?  I've been able
>> to find a terminal block that can handle more than 25A.  What is commonly
>> used as a connector for high current loads such as a motor?"
>>
>> There is a connector reffered to as a "Power-Pole" that is very popular in
>> modelling and Ham Radio that is very easy to find (not Radio Shack though)
>> in 15 and 20 AMP sizes. I am pretty sure they are available in larger sizes
>> as well.

You can get information on the PowerPole connectors from the Anderson Power web site. The size you are referring to uses a common housing which will take either 15, 30, or 45 Amp contacts. The main difference between the three is the size wire the contact will take. All three sizes will mate with one another.

Anderson also makes larger connectors used for fork lifts, etc. Up to 75 Amps, possible much more.

Tim

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>Donovan asked:  Can anyone suggest a connector to use that can handle 40A?

>I've been able to find a terminal block that can handle more than 25A.
>What is commonly used as a connector for high current loads such as a
motor?

Molex/Beau barrier strips  ( the 28 series) has conventional screw terminals
and a 50A rating

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> -----Original Message-----
> From: pic microcontroller discussion list
> [PICLISTMITVMA.MIT.EDU]On Behalf Of Welch, Ken
> Sent: Wednesday, 4 September 2002 4:14 AM
> To: PICLISTMITVMA.MIT.EDU
> Subject: Re: [EE]: Understanding Terminal Block Ratings
>
>
> >Donovan asked:  Can anyone suggest a connector to use that can
> handle 40A?
>
> >I've been able to find a terminal block that can handle more than 25A.
> >What is commonly used as a connector for high current loads such as a
> motor?
>
>
> Molex/Beau barrier strips  ( the 28 series) has conventional
> screw terminals
> and a 50A rating
Hi all,

I usually use "Din Rail" mounted terminals for high current (440VAC 3 phase
up to 100A) The ones I use by Klipon ? have Hex bolts (allen key style) and
I use a torque wrench to tighten them. Used to just do them till I felt they
were firm, but one was not quite, started to heat, then oxidise then heat
more till it melted open (and destroyed the terminal). I also use cable
ferales as with large sized cables and fine stands, it cuts out the odd
strand haning out and waiting to bite or flash at you.

Regards,

Kat.

**********************************************
K.A.Q. Electronics.
Electronic and Software Engineering.
Perth, Western Australia.
Ph +61 (0) 419 923 731
**********************************************
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Also try Automation Direct....good line of terminal blocks, DIN rail
mounted, and decent pricing.

>From: Katinka Mills <katinkaMAGESTOWER.COM>
>Reply-To: pic microcontroller discussion list <PICLISTMITVMA.MIT.EDU>
>To: PICLISTMITVMA.MIT.EDU
>Subject: Re: [EE]: Understanding Terminal Block Ratings
>Date: Wed, 4 Sep 2002 18:30:11 +0800
>
> > {Original Message removed}
On Mon, 2 Sep 2002, Sid Weaver wrote:

>The usual practice is to use "contactors", which are nothing more than
>high current relays.  They are available at Digikey at up to 100 amps.

So to pull the connector you cut the contactor in half ?

Peter

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