綜合布線的TT系統通常將電源中性點的接地叫做工作接地，而設備外露可導電部分的接地叫做保護接地。

綜合布線中TT系統的缺點

1)低、高壓線路雷擊時，配變可能發生正、逆變換過電壓

2)低壓電器外殼接地的保護效果不及IT系統。

3)當電氣設備的金屬外殼帶電(相線碰殼或設備絕緣損壞而漏電)時，由於有接地保護，可以大大減少觸電的危險性。但是，低壓斷路器(自動開關)不一定能跳閘，造成漏電設備的外殼對地電壓高於安全電壓，屬於危險電壓。

4)當漏電電流比較小時，即使有熔斷器也不一定能熔斷，所以還需要漏電保護器作保護，因此TT系統難以推廣。

5)TT系統接地裝置耗用鋼材多，而且難以回收、費工時、費料。

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Disadvantages of TT system in integrated wiring

1) When lightning strikes on low and high voltage lines, the transformer may undergo positive and negative transitions.

2) The protection effect of low-voltage electrical enclosure grounding is not as good as that of IT systems.

3) When the metal casing of the electrical equipment is charged (phase line is in contact with the casing or the insulation of the equipment is damaged and leaks), the risk of electric shock can be greatly reduced due to the grounding protection. However, the low-voltage circuit breaker (automatic switch) does not necessarily trip, causing the voltage of the earth leakage device to be higher than the safe voltage, which is a dangerous voltage.

4) When the leakage current is relatively small, even if there is a fuse, it may not be able to be blown, so the leakage protector is also required for protection, so the TT system is difficult to promote.

5) TT system grounding device consumes a lot of steel, and it is difficult to recycle, labor, and materials.

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