More than 64 devices on a line?

The only limitation is the power supply. 64 devices is not a law as I see it, it´s a recommendation based on the assumption that every device needs 10mA and you have 640mA power supply. In this case you seem to have power enough.

I would not recommend an installation like that. Exceeding with a few devices is normally not a problem but doubling cant be good. There´s a KNX-rule that there must be at least 200m between 2 power supplies but i cant explain why. Maybe someoneelse can shed light on this question.

it's not just power limit, there is also bus load limit. if you have lots of telegrams on line, you'll get repeated, also maybe lost telegrams. it all depends on devices on line and also on their configuration.

The requirements for length, number of devices, cable material and thickness and ... have been designed to have a reliable network (considered reflection, delays, latency, ...). As you may know all telegrams in KXN will be acknowledged (short ack), even when multiple devices are addressed. By not following the requirements of KNX spec you may be lucky and everythings work fine. But you may start to see problems and packet lost later when environmental condition changes and/or some other things change in your network.

As @hassan_mj says, you may be lucky and have it working so far, but it may stop working if conditions changes like, for instance, the devices involved in a group address.

The reason for the cable distances, materials and number of devices are related to ensuring communications. For instance, if you have a line segment with 64 devices and 1000mts of cable, not exceding 350mts between the power supply and the farest device, you would be in the limit of:

• the signal detection threshold: as cable & components impedance will attenuate the signal and thus having more cable and devices may translate in not being able of differentiating a '0' from a '1'
• the time a device can wait for an acknowledge telegram to be received before interpreting there's no acknowledge and retrying the sending: telegrams do not get instantly from one end of the line to the other, they take some time and, even if we talk about nanoseconds or milliseconds, the longer the distance, the longer the time, so you can have an installation where a device is unable to receive an ACK even if its telegram was received.

It is a tricky situation and cannot be guaranted to work.

Hope this helps. Regards.