Cisco 3850 switches - looking for specific measurements when flipping the rack ears

[ZPrime]

This is a really esoteric / specific question, but this forum is full of detail-oriented tech-minded people and I'm sure someone has this info or can easily get it.

I have been considering a Cisco Catalyst 3850, specifically the 24XU (24p mGig) or 12X48U (12p mGig, 36p 1Gb) to replace a Ubiquiti Edgeswitch 24 at home.
I don't have a real rack (yet), but I have a very deep 2U mount meant to handle a single patch panel and short-ish switch. I have a total depth of 16" available from rack ears to wallboard where this is sitting. I might be able to add a little more space by cutting out part of the wallboard, if I really have to (it's mounted across studs with nothing behind them).

Per Cisco's spec sheet, all of the Cat 3850s are these dimensions:
(H x W x D) 1.73 x 17.5 x 17.5 in. (4.4 x 44.5 x 44.5 cm) - (with the FAN FRUs installed but without the power supplies installed)
[I find it a little funny that they are square on one plane]

So obviously, 17.5" D > 16".
(I also know that the PSUs can stick out another 2-3 inches depending on the wattage.)

But, the rack ears on the switches are not lined up with the front of the switch. I believe in normal orientation, the front of the switch sticks out about an inch?

And, I know the rack ears can be flipped around... but how much of an offset does it give me if I flip the ears?

TL;DR: if you flip the rack ears backwards on a Catalyst 3850, what is the depth of the switch from the "inner" end of the rack ear to the back of the fan release tabs? How much space do you gain by flipping the ears?

 

[klui]

My swag where I just went on eBay to find one with a side profile, and with the ears flipped. Loaded into paint.net, display rulers (in inches), selected the portion I want and stretched the entire thing until it reached ~17.5".

 

[ZPrime]

Wow, how did I not even think of that...

Only problem with your method is that the 17.5" actually includes the fans, which stick out a bit from the rear. But I can probably repeat your method and figure this out, so thanks for the idea!

 

[klui]

Only problem with your method is that the 17.5" actually includes the fans

How do you figure? I measure from the top of the picture, not bottom. Fan not included.

 

[ZPrime]

How do you figure? I measure from the top of the picture, not bottom. Fan not included.

the actual Cisco spec sheet says:

(H x W x D) 1.73 x 17.5 x 17.5 in. (4.4 x 44.5 x 44.5 cm) - (with the FAN FRUs installed but without the power supplies installed)
So the manufacturer claims the "tips" on the backs of the fans are part of the 17.5".

 

[klui]

Oh I see, I missed that detail. I thought you were referring to the PSUs while responding about fans. Unfortunately the pictures don't show the fans. They look similar to my Juniper's fans which protrude out 1.5".

I am curious about what the idle power consumption is. Especially 24-port vs. 48-port. Pretty affordable full multi-gig switch, unlike my ICX 7150 which doesn't have 5 Gb. It's too bad the 48-port only has 12 mGig.

 

[BoGs]

I was looking at this switch as well as a 24 port AP POE switch but the specs for power do not give me hope. Where (no more then) 229 for 0 percent traffic and 248 for 100% traffic. I am not sure of the idle specs as Cisco does its own thing.

WS-C3850-24XU

C3850-NM-8-10G

229.7

231.2

248.1

232.7

 

[BoGs]

Never mind those seem to be the idle values? cannot be right. 229 w idle WOW.

Power consumption of standalone Cisco Catalyst 3850 Series Switches

Table 15 shows power consumption of standalone Cisco Catalyst 3850 Series Switches based on Alliance for Telecommunications Industry Solutions (ATIS) testing using IMIX distribution stream traffic, with input voltage of 115VAC at 60 Hz and no PoE loading. The values given are the maximum possible power consumption numbers under the respective test scenarios.

 

[klui]

Interesting. The 48U's idle power is 191W, inline with the VDX6740T.

OP is mistaken on the dimension. The link referred to does not include the 24XU/48XU.

Cisco Catalyst 3850 Series Switches Data Sheet is the unified datasheet and those switches have 19.2" depth. This datasheet does not state fans/PSUs are included with the measurements, but it is a good assumption that they do.

 

[ZPrime]

Interesting. The 48U's idle power is 191W, inline with the VDX6740T.

OP is mistaken on the dimension. The link referred to does not include the 24XU/48XU.

Cisco Catalyst 3850 Series Switches Data Sheet is the unified datasheet and those switches have 19.2" depth. This datasheet does not state fans/PSUs are included with the measurements, but it is a good assumption that they do.

You're right, the page I linked in the OP doesn't have a separate line for the mGig models. Yours does split them out.

I'm wondering if the chassis are actually all the same, and the only difference here is which PSU is included in the measurement. I know that the 1100W PSU that comes with the 48P PoE versions and presumably also with the mGig switches is really long... I was hoping maybe I could run the mGig switch with the 715W PSU (which I believe is shorter), as long as I don't need PoE on all the ports. I'm only using PoE on maybe 5-7 ports.

 

[BoGs]

I have looked at mGig POE and they are all power monsters that I am unwilling to put in the house. So I ran SMF everywhere and I spent that money on smaller switches for devices. Wifi so far is not a problem and I am waiting for newer, less power hoping mGig will be less demanding.

 

[ZPrime]

I have looked at mGig POE and they are all power monsters that I am unwilling to put in the house. So I ran SMF everywhere and I spent that money on smaller switches for devices. Wifi so far is not a problem and I am waiting for newer, less power hoping mGig will be less demanding.

That's too bad on the power & great for you on the fiber.
I don't have the time or money or space to pull fiber, and while the idle draw of the switch is a bit higher than I'd like, I believe it's still less power draw than running multiple switches. My gear is in a crawlspace and under some stairs, so the sound isn't a huge problem nor is any heat it generates.

 

[TeeJayHoward]

Cisco WS-C3850-48U-L w/ 1x PSU fully inserted (in case you have a hard stop at 16")
The fans jut out 1.5" from the back of the case, so less than the PSU does.
Also note that the PSU requires a notched cable (IEC320 C15), just in case you were thinking of using a right-angle one.

 

[klui]

How is the noise and does the idle wattage match the datasheet? The wattage would depend on what module you have installed:

4x1G: 115W
2x10G: 117W
4x10G: 120W

 

[TeeJayHoward]

How is the noise and does the idle wattage match the datasheet?

I can't speak to the wattage as I don't have a per-plug monitoring PDU (what IS the right term for that?) and my kill-a-watt is measuring the whole "server room". Noise is acceptable. It's not silent, but it's also not "datacenter loud". If this switch were in a closet with the door closed, I couldn't tell you if it was plugged in or not.

 

[klui]

I am tempted to get one... but I have too many switches. I don't have any Cisco in my lab and this could be my first. The temptation is these support higher power PoE and allows 2.5, 5, and 10G PoE. The disadvantage is Cisco's UPoE (60W) is not compliant with 802.3bt and in order to use more capable APs that can use faster than gigabit interfaces they would probably require PoE++ which this switch doesn't support. And I'm not about to get more Cisco stuff.

Are the right to use licenses embedded within the unit's FRU and all I need to do is to reactivate them after an OS reinstall? Many of the listings on eBay only shows the inventory and while there is a description that shows the model with license suffix, I haven't seen any show the right-to-use license. Is it common show license right-to-use usage output would be different from inv? I am aware you can activate a temporary 90-day license but not sure doing that could change the inv output.

 

[ZPrime]

Spoiler: inline picture

View attachment 39891

Cisco WS-C3850-48U-L w/ 1x PSU fully inserted (in case you have a hard stop at 16")
The fans jut out 1.5" from the back of the case, so less than the PSU does.
Also note that the PSU requires a notched cable (IEC320 C15), just in case you were thinking of using a right-angle one.

Thank you, this is really helpful. Combining it with the spec sheet linked earlier, I think it's pretty safe to say that the 19.2" depth in the datasheet includes the PSU. Given that I have 16" available... if I flip the ears backwards, the switch itself is only ~11", plus another 3-3.25" for the longest PSU and cord. So it should fit, although I won't be able to swap the PSU without removing the switch, unless I cut my plywood between the studs (which I'm not entirely against).

I'm aware of the notched cord requirement - I believe it's only there with the 1100W PSU, which is what these switches normally ship with... but I'm pretty sure they will operate with the lower power 710W PSU (also shorter, and I think doesn't require the notched power cord).

 

[arnbju]

Are the right to use licenses embedded within the unit's FRU and all I need to do is to reactivate them after an OS reinstall?

At some some version of IOS XE, Cisco stopped enforcing licenses. But i don't remember when the change happened.

 

[TeeJayHoward]

I'm aware of the notched cord requirement - I believe it's only there with the 1100W PSU, which is what these switches normally ship with... but I'm pretty sure they will operate with the lower power 710W PSU (also shorter, and I think doesn't require the notched power cord).

The 715W PSU IS indeed shorter. It fits entirely inside the switch, although the plate at the bottom of the PSU still juts out 1.5", like the fans. Here's the C3850-24XS-E sitting on top of the previous C3850-48U-L . The cord is still notched in the 715W PSU.

 

[Rdel70]

At some some version of IOS XE, Cisco stopped enforcing licenses. But i don't remember when the change happened.

latest version not requiring the "Smart Licensing" (aka phone home) is
cat3k_caa-universalk9.16.06.09.SPA.bin

Smart Licensing scheme is mandatory, starting with IOS-XE 16.9.1 and above

9.16.06.09 has been rock solid, no reason to upgrade past this version if you're not in an enterprise env with a support contract