In the system that I am designing, the peak current that the system requires is 80A at 36V DC. The terminal blocks that are available on the market are rated for 300V 30A. I want to know if the terminal rating is calculated based on the power that it can handle or only the current it can handle irrespective of the voltage rating.
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4The Joule effect depends solely on intensity (amperes)… – jcaron Dec 21 '21 at 08:19
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8the voltage limit is based on the plastic, the current limit is based on the metal. – dandavis Dec 21 '21 at 08:20
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Probably not. How short in time is your peak? – winny Dec 21 '21 at 08:20
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What's your RMS current? That's relevant to heating of conductors in series, like the wiring and the terminal block. – Neil_UK Dec 21 '21 at 08:21
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if the 2.5x current only happens for 1% of the time and the rest it's below max, it should be ok. – dandavis Dec 21 '21 at 08:23
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1You wouldn’t use the 300V in a power calculation, you would use the voltage drop across the terminal block, which would be a lot lower. – HandyHowie Dec 21 '21 at 08:25
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1Make one: flattened copper pipe mounted on insulators. – Solar Mike Dec 21 '21 at 08:35
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1If the load can be fused with a 30A fuse (even a slo-blo), then the terminal block is probably okay. – Spehro Pefhany Dec 21 '21 at 08:36
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1Once you find a suitable terminal block, remember to observe the torque specification also. 80A bolt connections need to be pretty tight. – jpa Dec 21 '21 at 18:57
2 Answers
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Your second premise is correct as with any connectors, it can handle only the maximum ratings in each respect alone.
So no going over the current spec because the voltage is lower.
Study the datasheet carefully, because sometimes there are derating curves, so that for the maximum rated voltage the maximum current is lower or AC/DC differences.
Some parts are also able to handle a pulsed current, so a brief overload may be okay. But again this has to be specified. (it likely isn't so reaching out to the manufacturer is often helpful)
Arsenal
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The application using a terminal block should keep within all of the block ratings. That is, it should have a lower Voltage, lower Current and lower Power.
Now there may be some wriggle room in the ratings themselves. The 30 A current rating would be for continuous current. If the duration of an intermittent higher current is much less than the thermal time constant of the terminals, so the temperature of the terminals changes little during the pulse, then there may be a case for asking the manufacturer if the block has a pulse rating. The RMS of the pulsey current waveform would have to stay below 30 A to keep long term control of temperature.
That's the physics of the situation, and applicable if you're doing a one-off hobby build in a non-critical place. If insurance could be involved, then using a connector at way over specification is guaranteed to get your claim turned down, even it's not directly involved with whatever went wrong.
Neil_UK
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