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Old 19-09-2021, 14:33   #1
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Are tee's ok on NEMA 2000 drop cables?

Hello all,

I am replacing the display heads over our companionway and will have several N2k displays within inches of each other. Is it ok to tee them off a common drop cable? The geography makes it unwieldy to run multiple drop cables (very narrow channel to run cable) and I prefer not to dead-end the backbone there.

I know that this is the purpose of the Maretron Multiport but it seems overkill (and $$$) for my needs.

Thanks in advance for your help,

Peter
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Old 19-09-2021, 19:12   #2
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Re: Are tee's ok on NEMA 2000 drop cables?

No but just as easy to extend the backbone to the location you want. Add multiple T’s to the backbone extension there and put the terminator back on the end of the last T.
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Old 19-09-2021, 21:10   #3
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Re: Are tee's ok on NEMA 2000 drop cables?

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Originally Posted by serendipitous View Post
Hello all,

I am replacing the display heads over our companionway and will have several N2k displays within inches of each other. Is it ok to tee them off a common drop cable? The geography makes it unwieldy to run multiple drop cables (very narrow channel to run cable) and I prefer not to dead-end the backbone there.

I know that this is the purpose of the Maretron Multiport but it seems overkill (and $$$) for my needs.

Thanks in advance for your help,

Peter
You can’t do that. If there’s room for two cables, loop the backbone through that area and back, with 2-port or 4-port T-connectors. If there’s only room for one cable, use the Maretron 4-port multidrop.
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Old 19-09-2021, 21:26   #4
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Re: Are tee's ok on NEMA 2000 drop cables?

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Old 20-09-2021, 02:13   #5
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Re: Are tee's ok on NEMA 2000 drop cables?

Actually in practice CAN bus at 250 kB/s is very tolerant of “ unusual “ bus wiring

So it will work
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Old 20-09-2021, 06:51   #6
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Re: Are tee's ok on NEMA 2000 drop cables?

Goboatingnow is correct that it will "probably" work, especially since most boat networks are not at the extreme limits of NMEA 2000 capabilities and your instruments are close together. To be officially correct, you need to have multiple drops or get a multi drop box such as the maretron multiport box.
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Old 20-09-2021, 09:34   #7
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Re: Are tee's ok on NEMA 2000 drop cables?

Officially everything I've read says NO but that is in effect what the Marlon box seems to be doing, and it is theoretically NMEA approved.

Are you planning to attach the displays directly to the 'T's?

As mentioned previously, a loop of backbone cable would eliminate any potential issue of using 'T's on drop cables and not require a terminator. If you don't have the space for a loop, ANCOR has 90 degree connectors. Two of these would turn you around in a tighter space. Or you may be able to just run the backbone all the way across.
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Old 20-09-2021, 09:36   #8
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Re: Are tee's ok on NEMA 2000 drop cables?

Ähm. Why do you think they sell it?
As long as you stay on one backbone it is no problem but do not use a T on another T-line
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Old 20-09-2021, 09:44   #9
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Re: Are tee's ok on NEMA 2000 drop cables?

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but that is in effect what the Marlon box seems to be doing, and it is theoretically NMEA approved.
I would think that the maretron multiport box had electronics inside to avoid the power loss and reflection problems that would otherwise occur.
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Old 20-09-2021, 09:48   #10
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Re: Are tee's ok on NEMA 2000 drop cables?

Following. Our 0183 network is dated and showing signs of needed upgrade.
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Old 20-09-2021, 10:00   #11
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Re: Are tee's ok on NEMA 2000 drop cables?

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Ähm. Why do you think they sell it?
As long as you stay on one backbone it is no problem but do not use a T on another T-line
Ahm. If you read the description, it says it connects to the backbone via a 'T'. That makes the box 4 'T's on a 'T'. . .
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Old 20-09-2021, 10:06   #12
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Re: Are tee's ok on NEMA 2000 drop cables?

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I would think that the maretron multiport box had electronics inside to avoid the power loss and reflection problems that would otherwise occur.
Possibly, but when I looked at the specifications page and wiring diagram on their website, I did not see any mention of such additional wiring. The diagram just shows all the lines connected directly to the drop cable. They could have omitted these details for 'proprietary' reasons. . .
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Old 20-09-2021, 11:35   #13
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Re: Are tee's ok on NEMA 2000 drop cables?

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Originally Posted by serendipitous View Post
Hello all,

I am replacing the display heads over our companionway and will have several N2k displays within inches of each other. Is it ok to tee them off a common drop cable? The geography makes it unwieldy to run multiple drop cables (very narrow channel to run cable) and I prefer not to dead-end the backbone there.

I know that this is the purpose of the Maretron Multiport but it seems overkill (and $$$) for my needs.

Thanks in advance for your help,

Peter
I work for Maretron, and you can do what you're suggesting, though it is not the ideal/best way of doing things. Just do NOT add another terminator on the end of that multi-tee drop cable. There should only be two terminators, one on each end of the main backbone.

Maretron has a free tool called N2KBuilder. It allows you to graphically lay out your network, and it will warn you of any potential issues. It's not only for Maretron devices, it supports any NMEA 2000 device as long as you can provide information such as the device instance and LEN (load equivalence number). You can download it from Maretron's website at https://www.maretron.com/products/N2KBuilder.php

Regards,
David
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Old 20-09-2021, 11:39   #14
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Re: Are tee's ok on NEMA 2000 drop cables?

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I would think that the maretron multiport box had electronics inside to avoid the power loss and reflection problems that would otherwise occur.
No electronics, just a more compact and secure way of connecting multiple devices, instead of stringing together multiple tees. It's electrically the same a 4 regular tees.
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Old 20-09-2021, 12:14   #15
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Re: Are tee's ok on NEMA 2000 drop cables?

Thanks for the info all.

It sounds like the most correct way is to route the backbone to above the companion way. Unfortunately in my case, the existing channel through the cabin side is bare thick enough for the two SeaTalk1 cables that go there now and simply wont accommodate two legs of a backbone.

I will either use the Maretron Multiport or dead-end (and terminate) the backbone there. Unfort7nately this means a lengthy loop of backbone to serve the instruments at the pedestal and stern and back again amidships to the companionway…

Oh well… if boats were easy everyone would be doing it…
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