Switching

The subject says it all: Why can I not mix power supplies in the EX4300(-32F)? I want DC and AC!!!

The hardware guide says one can only use AC or DC, but from an electrical (and my) point of view, the secondary side (the one facing the switch) should be identical regardless of the input power type. What is the problem here, really? Has anyone run the AC-DC combo in the EX4300 or similar switch? I'd be wiling to try myself, but cannot recommend it to a customer without more info.

Well, here it is clearly stated that you should avoid mixing AC and DC power in the same chassis - 

https://www.juniper.net/documentation/us/en/hardware/ex4300/topics/topic-map/ex4300-power-system.html

I believe there are very specific reasons why AC+DC setup is not recommended for any other equipment, not only this model.

The subject says it all: Why can I not mix power supplies in the EX4300(-32F)? I want DC and AC!!!

The hardware guide says one can only use AC or DC, but from an electrical (and my) point of view, the secondary side (the one facing the switch) should be identical regardless of the input power type. What is the problem here, really? Has anyone run the AC-DC combo in the EX4300 or similar switch? I'd be wiling to try myself, but cannot recommend it to a customer without more info.

Yes, it is clearly documented, so no issues there, but I guess I'm a bit frustrated since I cannot see an electrical problem mixing the two. Grounding and cabling could be one issue, but hardly on modern hardware. There are other switch brands that allow this in certain models but not in other (Nokia SAS-S does not, SAS-Mxp does).

Electrically, an AC feed to a switching power supply (which all are today in this product segment) is rectified to DC the first thing that happens in the PSU, so from there on, it is a DC PSU anyway, just with a higher voltage than a -48 VDC PSU.

As I said, perhaps more frustrated than expecting Juniper to change their policy... If anyone with real hard core electronics knowledge can shed some light, I'm all ears!

Well, here it is clearly stated that you should avoid mixing AC and DC power in the same chassis - 

https://www.juniper.net/documentation/us/en/hardware/ex4300/topics/topic-map/ex4300-power-system.html

I believe there are very specific reasons why AC+DC setup is not recommended for any other equipment, not only this model.

The subject says it all: Why can I not mix power supplies in the EX4300(-32F)? I want DC and AC!!!

The hardware guide says one can only use AC or DC, but from an electrical (and my) point of view, the secondary side (the one facing the switch) should be identical regardless of the input power type. What is the problem here, really? Has anyone run the AC-DC combo in the EX4300 or similar switch? I'd be wiling to try myself, but cannot recommend it to a customer without more info.

Yes, it is clearly documented, so no issues there, but I guess I'm a bit frustrated since I cannot see an electrical problem mixing the two. Grounding and cabling could be one issue, but hardly on modern hardware. There are other switch brands that allow this in certain models but not in other (Nokia SAS-S does not, SAS-Mxp does).

Electrically, an AC feed to a switching power supply (which all are today in this product segment) is rectified to DC the first thing that happens in the PSU, so from there on, it is a DC PSU anyway, just with a higher voltage than a -48 VDC PSU.

As I said, perhaps more frustrated than expecting Juniper to change their policy... If anyone with real hard core electronics knowledge can shed some light, I'm all ears!

Well, here it is clearly stated that you should avoid mixing AC and DC power in the same chassis - 

https://www.juniper.net/documentation/us/en/hardware/ex4300/topics/topic-map/ex4300-power-system.html

I believe there are very specific reasons why AC+DC setup is not recommended for any other equipment, not only this model.

The subject says it all: Why can I not mix power supplies in the EX4300(-32F)? I want DC and AC!!!

The hardware guide says one can only use AC or DC, but from an electrical (and my) point of view, the secondary side (the one facing the switch) should be identical regardless of the input power type. What is the problem here, really? Has anyone run the AC-DC combo in the EX4300 or similar switch? I'd be wiling to try myself, but cannot recommend it to a customer without more info.

Have you had any clarification on this yet?  

I'm interested in this as well.  I have a scenario where I'm switching over from an EX3300 to EX3400.  Ideally, I'd like to power up the EX3400 with a single AC power supply, then swap out all the connections from the old.  Once I've confirmed everything is working properly, I would install a DC power supply, then move the DC power over from the old to the new , remove the AC power supply and install the second DC.

If this works, it would minimize downtime.  If I had to revert to the old, I could have both switches powered up at the same time without having to wait for reboot.  Also, the DC power connections are different. The EX3300 is ring terminal vs the EX3400, which requires me to cut out the old terminal and wire up to a molex type terminal - not easy if I have to revert back.  

Other than Juniper stating that it should not be done, I don't see why this wouldn't work, but would like to know if there's something I'm not thinking about.

Yes, it is clearly documented, so no issues there, but I guess I'm a bit frustrated since I cannot see an electrical problem mixing the two. Grounding and cabling could be one issue, but hardly on modern hardware. There are other switch brands that allow this in certain models but not in other (Nokia SAS-S does not, SAS-Mxp does).

Electrically, an AC feed to a switching power supply (which all are today in this product segment) is rectified to DC the first thing that happens in the PSU, so from there on, it is a DC PSU anyway, just with a higher voltage than a -48 VDC PSU.

As I said, perhaps more frustrated than expecting Juniper to change their policy... If anyone with real hard core electronics knowledge can shed some light, I'm all ears!

Well, here it is clearly stated that you should avoid mixing AC and DC power in the same chassis - 

https://www.juniper.net/documentation/us/en/hardware/ex4300/topics/topic-map/ex4300-power-system.html

I believe there are very specific reasons why AC+DC setup is not recommended for any other equipment, not only this model.

The subject says it all: Why can I not mix power supplies in the EX4300(-32F)? I want DC and AC!!!

The hardware guide says one can only use AC or DC, but from an electrical (and my) point of view, the secondary side (the one facing the switch) should be identical regardless of the input power type. What is the problem here, really? Has anyone run the AC-DC combo in the EX4300 or similar switch? I'd be wiling to try myself, but cannot recommend it to a customer without more info.

Have you had any clarification on this yet?  

I'm interested in this as well.  I have a scenario where I'm switching over from an EX3300 to EX3400.  Ideally, I'd like to power up the EX3400 with a single AC power supply, then swap out all the connections from the old.  Once I've confirmed everything is working properly, I would install a DC power supply, then move the DC power over from the old to the new , remove the AC power supply and install the second DC.

If this works, it would minimize downtime.  If I had to revert to the old, I could have both switches powered up at the same time without having to wait for reboot.  Also, the DC power connections are different. The EX3300 is ring terminal vs the EX3400, which requires me to cut out the old terminal and wire up to a molex type terminal - not easy if I have to revert back.  

Other than Juniper stating that it should not be done, I don't see why this wouldn't work, but would like to know if there's something I'm not thinking about.

Yes, it is clearly documented, so no issues there, but I guess I'm a bit frustrated since I cannot see an electrical problem mixing the two. Grounding and cabling could be one issue, but hardly on modern hardware. There are other switch brands that allow this in certain models but not in other (Nokia SAS-S does not, SAS-Mxp does).

Electrically, an AC feed to a switching power supply (which all are today in this product segment) is rectified to DC the first thing that happens in the PSU, so from there on, it is a DC PSU anyway, just with a higher voltage than a -48 VDC PSU.

As I said, perhaps more frustrated than expecting Juniper to change their policy... If anyone with real hard core electronics knowledge can shed some light, I'm all ears!

Well, here it is clearly stated that you should avoid mixing AC and DC power in the same chassis - 

https://www.juniper.net/documentation/us/en/hardware/ex4300/topics/topic-map/ex4300-power-system.html

I believe there are very specific reasons why AC+DC setup is not recommended for any other equipment, not only this model.

The subject says it all: Why can I not mix power supplies in the EX4300(-32F)? I want DC and AC!!!

The hardware guide says one can only use AC or DC, but from an electrical (and my) point of view, the secondary side (the one facing the switch) should be identical regardless of the input power type. What is the problem here, really? Has anyone run the AC-DC combo in the EX4300 or similar switch? I'd be wiling to try myself, but cannot recommend it to a customer without more info.

The subject says it all: Why can I not mix power supplies in the EX4300(-32F)? I want DC and AC!!!

The hardware guide says one can only use AC or DC, but from an electrical (and my) point of view, the secondary side (the one facing the switch) should be identical regardless of the input power type. What is the problem here, really? Has anyone run the AC-DC combo in the EX4300 or similar switch? I'd be wiling to try myself, but cannot recommend it to a customer without more info.

I would caution against recommending this to a customer as a solution.

There is more to power supplies than just input and output. There are system level considerations ranging from power redundancy / load sharing dependencies to thermal, grounding and EMC compliance considerations. The power supplies were not designed for AC/DC (great name for a band, BTW! :)) mix-and-match configuration. Nor is the EX4300 system tested and qualified with this power configuration. It may appear to work when it is first set up, but over time and across scale, there may be unpredictable corner case issues that come up. 

Furthermore, it will be difficult for Juniper support teams to support any customer who deploys this unsupported power configuration. JTAC and support labs will not have this configuration available for testing. 

If there is a significant business case / need for supporting mix-and-match on EX4300, I would suggest kindly reach out to EX-Seies PLM / Product Management leads. With their backing, it might be possible to define a JVD for the mix-and-match case and have that fully tested by Juniper Test teams. This will give us a chance to find and fix any corner case issues before it hits the customer. 

Thanks!

The subject says it all: Why can I not mix power supplies in the EX4300(-32F)? I want DC and AC!!!

The hardware guide says one can only use AC or DC, but from an electrical (and my) point of view, the secondary side (the one facing the switch) should be identical regardless of the input power type. What is the problem here, really? Has anyone run the AC-DC combo in the EX4300 or similar switch? I'd be wiling to try myself, but cannot recommend it to a customer without more info.