General tips

Minimum bend radius of cables

Bending any kind of electrical cable, including coax, can cause internal breakage of the individual conductive strands that make up each wire (see attached diagram). A single strand breaking doesn’t necessarily stop the cable from functioning, but it does impact its ability to pass current by increasing the electrical resistance of the cable. Over time and with repeated bending, more and more strands will break until the current is too restricted to transmit power or data effectively. You may have encountered this issue with a personal USB cable for charging your phone, for instance. Think of it as bending a copper pipe back and forth until it breaks apart; at first, it may impede, but still allow the flow of water, but eventually the pipe breaks enough – or entirely – such that water can no longer flow freely through the whole length of the pipe.

For USB cables, which have multiple conductors, the minimum bend radius is 7 times the cable radius which is about 2.5 mm for most that we use. That said, you don’t need to measure every bend in all your cables, that would be a huge waste of time. Just be aware of this issue and try to keep them from kinking/don’t zip or twist tie them tightly.

SensorGnomes with the BBBK computer were built using the shortest possible cable (18 cm) to save on space and to keep cables tidy, but the size forces them to be bent beyond their recommended turn radius (see image attached). That means they are already under stress to start with and repeated use just exacerbates this problem. Using slightly longer cables will help fix this problem, but very long cables run into another problem where it’s easier to have a damaged cable without noticing since a cut or a kink will be harder to see.

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