NetMetal takes passive 24V PoE input and can be powered by a passive 24V PoE injector. The cAP ether2 port is supposed to be passive PoE up to 57v. The cAP senses the NetMetal load but the NetMetal will not power up. I have tried auto PoE and PoE on but neither works. Any suggestions about why and should it be possible?
Exactly which Netmetal model are you referring to ?
I looked at Netmetal AX and it only accepts POE in with 12-28V.
Netmetal 5: POE in with 8-30V as input.
If you use power adapter from cAP AX, that’s delivered with a 48V PSU in the box.
Which means also 48V on POE Out (give or take some differences).
You see the problem coming here ? Way too high.
The only thing you could try is to use a 24V PSU for cAP AX but then you might not get enough power for the second hop.
cAP AX only gives POE Out 600mA in the range 18-30V so with 24V that’s about 14.4W.
Netmetal AX can go up to 28W (base 12W) → tricky and definitely not ok if it goes full power.
Netmetal 5 can go up to 19W (no indication of nominal power but should be order of magnitude 10W, I guess). → might work, might not.
Or some POE splitter which converts that 48V level to 24V or so.
I only hope you did not fry that Netmetal yet applying 48V to it…
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I have a NetMetal AX which, as you say, takes 18-28V passive PoE input. The cAP takes 18-57V af/at input and outputs “Passive PoE up to 57V” per Mikrotik documentation. The cAP is powered by PoE in from a RB5009UPr+S+ which is supplying 48.7V, between 6-9W. I know that passive does not negotiate the voltage but “up to” implies that it isn’t a fixed voltage. It doesn’t fry the NetMetal, but also does not power it up. It might be because it cannot deliver the need wattage to even boot up.
Primary problem is the applied voltage.
If that cAP AX is powered from 48V coming from RB5009, it means there is (give or take) 48V coming out of ether2 on cAP AX.
That’s still too high for your Netmetal. So it will not even try to boot.
Even if you can solve that voltage problem, you will run into the power restriction.
This needs to be disambiguated.
NO Mikrotik device has any kind of voltage converter.
If you supply 48V to it, it will give 48V out (IF it is compatible up to 57 V).
If you supply 24 V to it, it will give 24V out.
In a nutshell, a PoE in device taking input at 18-28V cannot be powered at 48V, and a device powered at 48V will ONLY output on PoE the same 48V it gets.
That’s what I am trying to make clear from the beginning …
Yep, I am just trying to strengthen your message. 
BTW, it is loosely point #19 here:
Thanks to both of you. It makes sense that what is supplied is what is output. It was the wording in the MT literature “up to” that confused me. It is true, but would be clearer if it said “will output the input voltage up to 57V”. You both obviously know this but I am a software guy.